![48. The Hypothesis that Water is composed of
Separate Particles (Molecules).
It has been pointed out that we cannot see, and indeed that there is
not much hope of our ever being able to see, the separate particles of
water, even if water is composed of such particles. But it is perfectly
legitimate to suppose that water is made up of such particles, if that
hypothesis will enable us to explain the properties of water.
Let us suppose then that any portion of fluid water is really
composed of a prodigious number of particles less (and probably
much less) than a millionth of an inch in diameter. We may call these
particles molecules.[4]
4. Diminutive of moles, a mass.
We are justified, in accordance with the general properties of
matter (§ 18), in supposing that these molecules tend to approach
one another. But the fact that water is slightly compressible justifies
the supposition that its molecules are not in actual contact, but that
they are separated by interspaces, just as the motes in the air of a
dusty room are so separated.
What is it that keeps the molecules apart? We have seen that great
mechanical pressure brings them but slightly nearer to one another;
hence there is an equivalent resistance of some kind which keeps
them apart. This resistance must have the same origin as the
sensation which we know as heat, for it has been seen that
diminution of heat diminishes the bulk of water; that is, allows the
molecules to come closer together; that is, diminishes their tendency
to keep asunder. Increase of heat, on the other hand, increases the
volume of water; that is to say, drives the molecules further apart, or
increases their tendency to keep asunder.
Suppose we call the cause of the tendency of the molecules of
water to come together an attractive force; and the cause of their
keeping apart, which manifests itself to us as the sensation of heat
and is, as we have seen, in all probability, a rapid vibratory or
whirling motion of the molecules, a repulsive force; then, in the](https://image.slidesharecdn.com/9289-250505053930-941c9ff5/85/Test-Bank-for-Exploring-Lifespan-Development-2nd-Edition-Berk-38-320.jpg)
Test Bank for Exploring Lifespan Development, 2nd Edition: Berk
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- 5. Test Bank for Berk / Exploring Lifespan Development, 2/e 2 Copyright © 2011 Pearson Education, Inc. All Rights Reserved. Page Ref: 4 Skill: Conceptual Objective: 1.2
- 6. Chapter 1 History, Theory, and Research Strategies Copyright © 2011 Pearson Education, Inc. All Rights Reserved. 3 5) The ___________ view of development holds that infants and preschoolers respond to the world in much the same way as adults do. A) discontinuous B) nature C) continuous D) nurture Answer: C Page Ref: 4 Skill: Factual Objective: 1.2 6) Within the ________________ view of development, new ways of understanding and responding to the world emerge at specific times. A) discontinuous B) nature C) continuous D) nurture Answer: A Page Ref: 4 Skill: Factual Objective: 1.2 7) Dr. Kostel believes that development takes place in stages. This belief is consistent with the _________ perspective. A) nurture B) continuous C) discontinuous D) nature Answer: C Page Ref: 4 Skill: Applied Objective: 1.2 8) Kim is interested in comparing the language development of shy versus outgoing preschoolers. Kim is most likely interested in ______________ that shape development. A) genetic factors B) the contexts C) therapeutic techniques D) historical factors Answer: B Page Ref: 4 Skill: Applied Objective: 1.2 9) Jackson, a professional baseball player, is convinced that his two sons will both be outstanding athletes. Jackson probably believes that athletic ability is mostly determined by A) nurture. B) stages. C) early experiences. D) nature. Answer: D Page Ref: 5 Skill: Applied Objective: 1.2
- 7. Test Bank for Berk / Exploring Lifespan Development, 2/e 4 Copyright © 2011 Pearson Education, Inc. All Rights Reserved. 10) Although Justin spent his first 18 months in an orphanage, his adoptive mother believes that sensitive caregiving will help Justin overcome his early experiences. Justin’s mother emphasizes the role of ____________ in development. A) nurture B) stages C) stability D) nature Answer: A Page Ref: 5 Skill: Applied Objective: 1.2 11) Theorists who point to early experiences as establishing a lifelong pattern of behavior emphasize A) stages. B) discontinuity. C) stability. D) continuity. Answer: C Page Ref: 5 Skill: Factual Objective: 1.2 12) Theorists who believe that change is possible and even likely if new experiences support it emphasize A) stages. B) plasticity. C) nature. D) stability. Answer: B Page Ref: 5 Skill: Factual Objective: 1.2 13) The increase in the number of healthier, more active older adults suggests that human development is a A) controversial area of research. B) unidirectional system. C) dynamic system. D) biological, rather than environmental, science. Answer: C Page Ref: 5 Skill: Conceptual Objective: 1.3 14) Max, age 65, learned to play the piano at a local senior center. Max demonstrates that A) aging is an eventual “shipwreck.” B) learning follows a predictable timetable. C) development is plastic at all ages. D) musical talent peaks in late adulthood. Answer: C Page Ref: 5 Skill: Applied Objective: 1.3
- 8. Chapter 1 History, Theory, and Research Strategies Copyright © 2011 Pearson Education, Inc. All Rights Reserved. 5 15) In the lifespan perspective, every age period of human development A) has its own agenda and its unique demands and opportunities that yield some similarities in development across many individuals. B) is met with a significant crisis that must be overcome prior to moving on to the next age period. C) is unidirectional and marked by improved performance. D) has a greater impact on the life course than the previous age period. Answer: A Page Ref: 5–6 Skill: Conceptual Objective: 1.3 16) The lifespan perspective on development assumes that A) development is static and stable. B) events that occur during infancy and early childhood have the strongest impact on the life course. C) development is affected by a blend of biological, psychological, and social forces. D) individual development is continuous, rather than discontinuous. Answer: C Page Ref: 6 Skill: Conceptual Objective: 1.3 17) Which of the following is an assumption of the lifespan perspective? A) Development is largely the result of heredity. B) Development is primarily characterized by declines in functioning. C) Development is a joint expression of growth and decline. D) Plasticity is limited to early childhood. Answer: C Page Ref: 6 Skill: Conceptual Objective: 1.3 18) Which of the following is an example of an age-graded influence? A) Paul started babysitting at age 13. B) Frank got his driver’s license at age 16. C) Martina got married at age 34. D) Jesse learned to use a computer at age 21. Answer: B Page Ref: 7 Skill: Applied Objective: 1.3 19) Although Betty grew up in a rundown neighborhood, had divorced parents, and rarely saw her father, she is a successful, happy, and healthy adult. Betty’s ability to adapt effectively in the face of threats to development is known as A) assimilation. B) resilience. C) age-graded development. D) multidimensional development. Answer: B Page Ref: 8 Box: B&E: Resilience Skill: Applied Objective: 1.3
- 9. Test Bank for Berk / Exploring Lifespan Development, 2/e 6 Copyright © 2011 Pearson Education, Inc. All Rights Reserved. 20) Which of the following is a personal characteristic that could offer protection from the damaging effects of early stressful life events? A) musical talent B) hyperactivity C) physical attractiveness D) early puberty Answer: A Page Ref: 8 Box: B&E: Resilience Skill: Conceptual Objective: 1.3. 21) Research on resilience shows that A) heredity is more powerful than the environment in protecting children from the negative effects of stressful life events. B) the environment is more powerful than heredity in protecting children from the negative effects of stressful life events. C) interventions must attend to both the person and the environment to strengthen a child’s capacity while also reducing hazardous experiences. D) plasticity is limited to infancy and early childhood. Answer: C Page Ref: 8 Box: B&E: Resilience Skill: Conceptual Objective: 1.3 22) History-graded influences explain why ___________ tend to be alike in ways that set them apart from people born at other times. A) siblings B) coworkers C) cohorts D) friends Answer: C Page Ref: 9 Skill: Factual Objective: 1.3 23) Which of the following is an example of a nonnormative influence? A) Steve reached puberty at age 14. B) Melina was born during the baby boom. C) Madison learned to talk at age 2. D) Patty learned to speak Spanish and French in college. Answer: D Page Ref: 9 Skill: Applied Objective: 1.3 24) The increasing role of ______________ in the life course adds to the fluid nature of lifespan development. A) age-graded influences B) nonnormative events C) history-graded influences D) stagewise transformations Answer: B Page Ref: 9 Skill: Factual Objective: 1.3
- 10. Chapter 1 History, Theory, and Research Strategies Copyright © 2011 Pearson Education, Inc. All Rights Reserved. 7 25) As a generation, baby boomers are A) healthier, but less educated, than the previous generation. B) more educated and less self-focused than the previous generation. C) healthier, better educated, and more self-focused than the previous generation. D) more self-focused, but financially worse off, than the previous generation. Answer: C Page Ref: 10 Box: LV: The Baby Boomers Reshape the Life Course Skill: Conceptual Objective: 1.3 26) Research on the baby boomers showed that starting in the mid-sixties, A) marriage rates declined, age of first marriage rose, and divorce rates increased. B) marriage rates increased, age of first marriage declined, and divorce rates stabilized. C) fewer young people entered college in favor or marriage and parenthood. D) young adults experienced higher rates of unemployment and financial insecurity than in previous generations. Answer: A Page Ref: 10 Box: LV: The Baby Boomers Reshape the Life Course Skill: Conceptual Objective: 1.3 27) Today, __________ are the largest generation ever to enter middle age. A) emerging adults B) African-American adults C) the baby boomers D) college educated women Answer: C Page Ref: 10 Box: LV: The Baby Boomers Reshape the Life Course Skill: Factual Objective: 1.3 28) Charles Darwin’s theory of evolution emphasized ______________ and _______________. A) the normative approach; survival of the fittest B) noble savages; physical maturation C) natural selection; survival of the fittest D) tabula rasa; natural selection Answer: C Page Ref: 11 Skill: Conceptual Objective: 1.4 29) Charles Darwin’s theories led other researchers to study all aspects of children’s behavior and, therefore, Darwin is considered the forefather of A) psychoanalysis. B) the mental testing movement. C) psychosocial theory. D) scientific child study. Answer: D Page Ref: 11 Skill: Factual Objective: 1.4
- 11. Test Bank for Berk / Exploring Lifespan Development, 2/e 8 Copyright © 2011 Pearson Education, Inc. All Rights Reserved. 30) G. Stanley Hall regarded development as a _____________ process. A) maturational B) nonnormative C) psychosocial D) social learning Answer: A Page Ref: 11 Skill: Factual Objective: 1.4 31) G. Stanley Hall and his student, Arnold Gesell, A) discovered that prenatal growth is strikingly similar in many species. B) launched the normative approach. C) constructed the first standardized intelligence test. D) were the forefathers of psychoanalytic theory. Answer: B Page Ref: 11 Skill: Conceptual Objective: 1.4 32) _____________ was among the first to make knowledge about child development meaningful to parents by writing child- rearing books. A) G. Stanley Hall B) Charles Darwin C) Arnold Gesell D) Alfred Binet Answer: C Page Ref: 11–12 Skill: Factual Objective: 1.4 33) Alfred Binet and Theodore Simon’s intelligence test was originally constructed to A) measure individual differences in IQ. B) document age-related improvements in children’s intellectual functioning. C) identify children with learning problems who needed to be placed in special classes. D) compare the scores of people who varied in gender, ethnicity, and birth order. Answer: C Page Ref: 11–12 Skill: Conceptual Objective: 1.4 34) According to Sigmund Freud, the A) ego develops through interactions with parents. B) superego is the conscious, rational part of personality. C) ego is the largest portion of the mind. D) id is the source of basic biological needs and desires. Answer: D Page Ref: 12 Skill: Conceptual Objective: 1.5
- 12. Chapter 1 History, Theory, and Research Strategies Copyright © 2011 Pearson Education, Inc. All Rights Reserved. 9 35) In contrast to Sigmund Freud, Erik Erikson A) viewed children as taking a more active role in their own development. B) pointed out that normal development must be understood in relation to each culture’s life situation. C) minimized the role of culture in individual development. D) primarily focused on the importance of early life experiences. Answer: B Page Ref: 13 Skill: Conceptual Objective: 1.5 36) Behaviorism focuses on A) unconscious impulses and drives. B) stimuli and responses. C) natural selection and survival of the fittest. D) clinical case studies. Answer: B Page Ref: 13 Skill: Conceptual Objective: 1.5 37) In classical conditioning, A) a neutral stimulus is paired with another stimulus that produces a reflexive response. B) an innate reflex is extinguished. C) unconscious impulses and drives support healthy development. D) a reflexive response is paired with a new stimulus that produces a nonreflexive response. Answer: A Page Ref: 13–14 Skill: Conceptual Objective: 1.5 38) Baby Max begins to cry as soon as he sees his mother pick up her car keys. Max probably does this because he learned to associate the car keys with his mother leaving. This example demonstrates A) modeling. B) operant conditioning. C) observational learning. D) classical conditioning. Answer: D Page Ref: 13–14 Skill: Applied Objective: 1.5 39) In a historic experiment with 11-month-old Albert, John Watson demonstrated that A) children cannot be conditioned to fear a formerly neutral stimulus. B) infants as young as a few months old will repeat a behavior to obtain a desirable reward. C) children can be conditioned to fear a formerly neutral stimulus. D) children have an innate, inborn fear of rats. Answer: C Page Ref: 14 Skill: Conceptual Objective: 1.5
- 13. Test Bank for Berk / Exploring Lifespan Development, 2/e 10 Copyright © 2011 Pearson Education, Inc. All Rights Reserved. 40) According to _______ theory, the frequency of a behavior can be increased by following it with a wide variety of reinforcers. A) classical conditioning B) observational learning C) operant conditioning D) psychoanalytic Answer: C Page Ref: 14 Skill: Factual Objective: 1.5 41) Garrett hits a playmate in the same way that he has been punished at home. This is an example of A) behavior modification. B) classical conditioning. C) operant conditioning. D) modeling. Answer: D Page Ref: 14 Skill: Applied Objective: 1.5 42) According to ___________ theory, children learn primarily through modeling. A) reinforcement B) operant conditioning C) social learning D) classical conditioning Answer: C Page Ref: 14–15 Skill: Factual Objective: 1.5 43) According to social learning theory, as children grow older they A) become more selective in what they imitate. B) become less selective in what they imitate. C) imitate more than they model. D) respond more favorably to punishment than reinforcement. Answer: A Page Ref: 15 Skill: Conceptual Objective: 1.5 44) Behavior modification eliminates undesirable behaviors by A) exposing children to group therapy. B) having patients talk freely about painful childhood events. C) improving children’s social settings, such as school and home. D) combining conditioning and modeling. Answer: D Page Ref: 15 Skill: Conceptual Objective: 1.5
- 14. Chapter 1 History, Theory, and Research Strategies Copyright © 2011 Pearson Education, Inc. All Rights Reserved. 11 45) Albert Bandura is unique among behaviorists because he A) combined psychoanalytic principles with operant conditioning theory. B) emphasized cognition and granted people an active role in their own learning. C) emphasized the role of the unconscious on people’s learning. D) emphasized the importance of early child-rearing experiences. Answer: B Page Ref: 15 Skill: Conceptual Objective: 1.5 46) According to Jean Piaget, ___________ is the balance between internal structures and information that children encounter in their everyday worlds. A) modeling B) maturation C) cognition D) equilibrium Answer: D Page Ref: 15 Skill: Factual Objective: 1.5 47) Research on Piaget’s cognitive-developmental theory indicates that A) he overestimated the competencies of infants and young children. B) he overemphasized the role of social and cultural influences on development. C) discovery learning facilitates learning better than adult teaching. D) children’s performances on Piagetian tasks can be improved with training. Answer: D Page Ref: 16 Skill: Conceptual Objective: 1.5 48) The information-processing approach views the mind as a A) symbol-manipulating system through which information flows. B) socially mediated process. C) collection of stimuli and responses. D) system of genetically programmed behaviors. Answer: A Page Ref: 17 Skill: Factual Objective: 1.6 49) Lillian uses flowcharts to map the precise steps individuals use to solve problems and complete tasks. Lillian is a(n)__________ theorist. A) psychoanalytic B) information-processing C) dynamic systems D) social learning Answer: B Page Ref: 17–18 Skill: Applied Objective: 1.6
- 15. Test Bank for Berk / Exploring Lifespan Development, 2/e 12 Copyright © 2011 Pearson Education, Inc. All Rights Reserved. 50) Which of the following questions would an information-processing theorist ask? A) How do unconscious drives contribute to personality development? B) How do cultural values shape development? C) Are declines in memory during old age evident on all types of tasks or only some? D) Why are some individuals more aggressive than others? Answer: C Page Ref: 17–18 Skill: Applied Objective: 1.6 51) A major weakness of the information-processing perspective is that it A) overemphasizes nonlinear aspects of cognition, such as creativity and imagination. B) virtually ignores aspects of cognition that are not linear and logical. C) fails to use rigorous research methods. D) underestimates the individual’s contribution to his or her own development. Answer: B Page Ref: 18 Skill: Conceptual Objective: 1.6 52) __________ brings together researchers from psychology, biology, neuroscience, and medicine to study the relationship between changes in the brain and the developing person’s cognitive processing and behavior patterns. A) The information-processing approach B) Cognitive-development theory C) Developmental cognitive neuroscience D) Behaviorism Answer: C Page Ref: 18 Skill: Factual Objective: 1.6 53) __________ is concerned with the adaptive value of behavior and its evolutionary history. A) Ethology B) Developmental cognitive theory C) Social learning theory D) Psychoanalytic theory Answer: A Page Ref: 18 Skill: Factual Objective: 1.6 54) Dr. Marx believes that early childhood is a sensitive period for language development. Dr. Marx’s belief is consistent with A) social learning theory. B) Freud’s theory. C) ethology. D) Piaget’s theory. Answer: C Page Ref: 18 Skill: Applied Objective: 1.6
- 16. Chapter 1 History, Theory, and Research Strategies Copyright © 2011 Pearson Education, Inc. All Rights Reserved. 13 55) A(n) _________ period is a time that is optimal for certain capacities to emerge. A) equilibration B) imprinting C) adaptive D) sensitive Answer: D Page Ref: 19 Skill: Factual Objective: 1.6 56) John Bowlby argued that A) behaviors such as smiling, babbling, and crying are innate social signals that encourage parents to interact with their infants. B) infants become attached to their parents because parents are associated with the reduction of primary drives, such as hunger and thirst. C) parents and infants are both instinctively attached to each other. D) attachment patterns are difficult to study in humans. Answer: A Page Ref: 19 Skill: Conceptual Objective: 1.6 57) Dr. Symington studies male-to-male aggression in animals and humans. Dr. Symington probably focuses on A) dynamic systems theory. B) developmental cognitive theory. C) sociocultural theory. D) evolutionary developmental theory. Answer: D Page Ref: 19 Skill: Applied Objective: 1.6 58) Lev Vygotsky’s theory focuses on A) critical periods of human development. B) children’s capacity to shape their own development. C) how behavior patterns promote survival. D) how culture is transmitted to the next generation. Answer: D Page Ref: 19–20 Skill: Conceptual Objective: 1.6 59) _______________ theory views the child as developing within a complex system of relationships affected by multiple levels of the environment. A) Social learning B) Ethological C) Sociocultural D) Ecological systems Answer: D Page Ref: 20 Skill: Factual Objective: 1.6
- 17. Test Bank for Berk / Exploring Lifespan Development, 2/e 14 Copyright © 2011 Pearson Education, Inc. All Rights Reserved. 60) Because a child’s biologically influenced dispositions join with environmental forces to mold development, Urie Bronfenbrenner characterized his perspective as a(n) ______________ model. A) sociocultural B) stagewise C) bioecological D) evolutionary Answer: C Page Ref: 20 Skill: Factual Objective: 1.6 61) Bronfenbrenner’s macrosystem consists of A) activities and interaction patterns in the individual’s immediate surroundings. B) third parties that affect the quality of the parent–child relationship. C) cultural values, laws, customs, and resources. D) social settings that do not contain the developing person but nevertheless affect experiences. Answer: C Page Ref: 21 Skill: Conceptual Objective: 1.6 62) Toby moved with his family just before he entered grade 4. In ecological systems theory, the move represents a change in Toby’s A) microsystem. B) mesosystem. C) exosystem. D) chronosystem. Answer: D Page Ref: 21 Skill: Applied Objective: 1.6 63) Piaget’s cognitive-developmental theory, information processing, and Vygotsky’s sociocultural theory all stress A) nature over nurture. B) changes in thinking. C) unconscious motives and drives. D) the effects of punishment and reinforcement on behavior. Answer: B Page Ref: 21 Skill: Conceptual Objective: 1.7 64) Dr. George predicted that positive reinforcement would increase prosocial behavior in preschoolers. Dr. George’s prediction is an example of a A) theory. B) research question. C) hypothesis. D) research design. Answer: C Page Ref: 22 Skill: Applied Objective: 1.8
- 18. Chapter 1 History, Theory, and Research Strategies Copyright © 2011 Pearson Education, Inc. All Rights Reserved. 15 65) Dr. Wiren observes children’s responses to bullying by watching them play in a park. This is an example of a(n) A) ethnographic study. B) naturalistic observation. C) structured observation. D) clinical interview. Answer: B Page Ref: 23 Skill: Applied Objective: 1.8 66) A major limitation of systematic observation is that it A) provides little information on how participants actually behave. B) underestimates the capacities of individuals who have difficulty putting their thoughts into words. C) tells investigators little about the reasoning behind responses and behaviors. D) ignores participants with poor memories, who may have trouble recalling exactly what happened. Answer: C Page Ref: 23–24 Skill: Conceptual Objective: 1.8 67) Jessica asked each of 21 children in a kindergarten classroom to explain where rain comes from. She asked the same set of follow-up questions to each participant. This is an example of a A) field experiment. B) naturalistic observation. C) structured interview. D) structured observation. Answer: C Page Ref: 24 Skill: Applied Objective: 1.8 68) A __________ interview is more efficient than a _________ interview because researchers can obtain written responses from an entire group simultaneously. A) clinical; naturalistic B) structured; naturalistic C) clinical; structured D) structured; clinical Answer: D Page Ref: 24–25 Skill: Conceptual Objective: 1.8 69) ____________ interviews do not yield the same depth of information as ___________ interviews. A) Clinical; naturalistic B) Clinical; structured C) Structured; clinical D) Structured; naturalistic Answer: C Page Ref: 24–25 Skill: Conceptual Objective: 1.8
- 19. Test Bank for Berk / Exploring Lifespan Development, 2/e 16 Copyright © 2011 Pearson Education, Inc. All Rights Reserved. 70) One major limitation of the clinical, or case study, method is A) that researchers’ theoretical preferences may bias their observations and interpretations. B) that it must be conducted with large groups of people at the same time. C) it provides little information on how children and adults actually behave. D) it provides little information about the reasoning behind responses and behaviors. Answer: A Page Ref: 25 Skill: Conceptual Objective: 1.8 71) The __________ method yields richly detailed case narratives that offer valuable insights into the many factors influencing development. A) naturalistic observation B) clinical C) ethnographic D) structured observation Answer: B Page Ref: 25 Skill: Conceptual Objective: 1.8 72) Ethnographic research is directed toward understanding a culture through _____________ observation. A) naturalistic B) participant C) systematic D) structured Answer: B Page Ref: 25 Skill: Conceptual Objective: 1.8 73) The ethnographic method assumes that ______________ will allow researchers to understand beliefs and behaviors. A) entering into close contact with a social group B) bringing together a wide range of information on one person C) setting up a structured laboratory experiment D) using a flexible, conversational interviewing style Answer: A Page Ref: 25 Skill: Conceptual Objective: 1.8 74) Jade spent two years in a Mexican-American community studying communication between parents and children. Jade is using the ___________ research method. A) naturalistic observation B) ethnographic C) self-report D) structured observation Answer: B Page Ref: 25 Skill: Applied Objective: 1.8
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- 21. 36. Steam is an Elastic Fluid or Gas. In all the properties which have been mentioned water in the form of steam is an elastic fluid or gas like air. If a little water is placed in the flask mentioned in the preceding section all the “empty” part of the space will contain air. If the flask is now made hot the water will at length boil, bubbles of steam forming in the water and breaking at its surface. By degrees, the air, which at first lay above the water, will be driven out; and if the whole flask is kept hot, the “empty” part of it will be full of the gaseous water, which is transparent and colourless like air. The steam flows out of the mouth of the flask still a clear and colourless gas; but it soon cools and becomes condensed as a cloud of small particles of fluid water. Steam is lighter than air, and hence it rises in the air, just as bodies which are lighter than water rise in water.
- 22. 37. Gases and Vapours. Air is as much a gas in the coldest winter as it is in the hottest summer. But air can be liquefied by exposing it to a very low temperature, while, at the same time, it is subjected to an extremely great pressure. Thus, the difference between gases like air, which are condensed with extreme difficulty, and gases like steam, which are condensed easily, is only one of degree. Nevertheless there is a certain convenience in distinguishing those gases, which, like steam, are easily condensed as vapours. In what we ordinarily call steam, all the water of which it is composed remains gaseous only at and above the temperature of boiling water (212° Fahrenheit). Cooled ever so little below this point, most of it becomes condensed into hot liquid water. However, it must be recollected that though that particular form of gaseous water which we call steam exists only at and above the temperature of boiling water, yet water is capable of existing in the gaseous state down to the freezing-point. Suppose that when our boiling flask contained nothing but water and steam, the mouth were stopped and the lamp removed. Then, so long as the temperature of the whole remained at that of boiling water, every cubic inch of steam above the water in the flask would weigh about ⅐th of a grain, since 100 cubic inches weigh about 15 grains. Suppose the capacity of the flask, exclusively of the fluid water in it, to be 100 cubic inches. Then, to begin with, the gaseous water which it contains will weigh 15 grains. If the flask is now allowed to cool, more and more of the gaseous water condenses into the fluid state; but, even down to the freezing-point, some water will remain in the gaseous state and will fill that part of the flask which is unoccupied by the fluid water. At blood-heat (98°) the gaseous water weighs only about a grain, though it still occupies 100 cubic inches; at the ordinary temperature of the air it weighs not more than ⅓rd of a grain; while, at the freezing-point, its weight is only ⅛th of a grain. But inasmuch as there is less and less actual weight of water in the same volume of gaseous water as the temperature falls, it follows that the density, or specific gravity, of the gaseous water must be less the lower the temperature. Moreover, while, at the boiling-point,
- 23. gaseous water or steam resists compression with exactly the same force as air does, the lower the temperature the more easily compressible is the gaseous water. Suppose an elastic bag were to be tied on to the nozzle of a kettle full of boiling water. If the bag were kept as hot as the boiling water it would become fully distended, and maintain its shape in spite of the pressure of the air upon all sides of it. If the bag were taken away it would retain its shape so long as it was kept as hot as boiling water; but, if it were allowed to cool, it would gradually become flattened by the outside air squeezing up the less and less resisting gaseous water of the lower temperatures. Hence, when the stopped flask has been allowed to cool, the air rushes in with great violence if it is opened.
- 24. 38. The Evaporation of Water at ordinary Temperatures. If some water is poured into a saucer and is allowed to stand even in a cool room or in the open air, you know that it sooner or later disappears. Wet clothes hung on a line soon dry—that is to say, the water clinging to them disappears or evaporates. The disappearance of the water under these circumstances results from the property just mentioned. In fact, it becomes gaseous water of the density appropriate to the temperature, and as such mixes with the air as any other gas would do. And as the sea, lakes, and rivers, are constantly giving off gaseous water into the air in proportion to the temperature, it is not wonderful that the atmosphere always contains gaseous water. Air is said to be moist when the weight of water in a given quantity, say 100 cubic inches, is as much, or nearly as much, as can exist in the state of gas at the temperature. Under these circumstances, if the temperature is lowered even a very little, some of the gaseous water is converted into liquid water. We see this in hot moist weather, when the outside of a tumbler of fresh drawn cold spring water immediately becomes bedewed. The gaseous water in immediate contact with the tumbler, in fact, is cooled down below the point at which it can all exist as gas, and the superfluity is deposited as dew. In such days wet clothes do not dry well, because there is, already, nearly as much gaseous water in the atmosphere as the amount of heat marked by the thermometer can maintain in that state.
- 25. 39. When Hot Water is cooled, it Contracts to begin with, but after a time Expands. We have now seen what a wonderful change is brought about by heating water. At first, it expands gradually and slightly; but, when it reaches the boiling-point, it suddenly expands enormously, and is no longer a liquid, but a gas. On the other hand, if warm water is allowed to cool, it gradually contracts till it reaches the ordinary temperature of the air in mild weather; but, if the weather is very cold, or if the water is cooled artificially, it goes on contracting only down to a certain temperature (39°), and then begins to expand again. In this peculiarity water is unlike all other bodies which are fluid at ordinary temperatures. Hence the temperature of 39° is that at which pure water has its greatest density or specific gravity, and water at this temperature is heavier, bulk for bulk, than the same water at any other temperature. Therefore if water at the top of a vessel is cooled down to this temperature, it falls to the bottom, and if the water at the bottom of a vessel is cooled below this temperature it rises to the top.
- 26. 40. Water cooled still further becomes the transparent brittle solid Ice. Our tumbler of water, if put out of doors on a cold winter’s night, would gradually cool until it assumed a temperature of 39° throughout. Cooling below this temperature, the water so cooled would gradually accumulate at the surface by reason of its less density, and its temperature would fall till the thermometer placed in it marked 32°. As soon as this upper water cooled ever so little below 32°, a film like glass would form on its surface by the conversion of the coldest fluid water into solid water or ice. And if all the water cooled down to the same degree it would all gradually change into the same kind of substance. In this condition water is solid. It occupies space, offers resistance, has weight and transmits motion as the water did, but if you shake it out of the tumbler in a cold place it retains its form without the least change. If you press it, it proves to be exceedingly hard and unyielding; and, if the pressure is increased, it becomes crushed and breaks like glass. It may thus be crushed to powder, and the ice powder can be formed into heaps as if it were sand. Just as any quantity of steam has exactly the same weight as the water which was converted into it by heat; so the ice has exactly the same weight as the water which has been converted into it by taking away heat.
- 27. 41. Ice has less Specific Gravity than the Water from which it was formed. But though the ice in the tumbler has the same weight as the water had, it has not the same volume. The expansion which began at 39° goes on, and when water passes into the solid state its volume is about 1 11 th greater than it was at 39°. Taking water at this temperature as 1·0, ice has a specific gravity of 0·916. But although water in freezing expands only to this small amount, it resembles steam in the tremendous force with which it expands. If you fill a hollow iron shell quite full of water, screw down the opening tight, and then put it in a cold place where the water may freeze, the water as it freezes will burst the iron walls of the shell. You know that when the winter is severe, the pipes by which water is brought to a house often burst. This is because the water in them freezes, and, being unable to get out of the pipe, bursts it, just as you may burst a jacket that is too tight for you by stretching yourself. Among the bare hill-tops, or on the face of cliffs exposed to the weather, the strongest and hardest rocks are every winter split and broken, just as if quarrymen had been at work at them. In the summer the rain-water gets into the little cracks and rifts in the stone and lodges there. Then the winter comes with its cold and freezes the water. And the water bursts the rocks asunder just as it bursts our waterpipes.
- 28. 42. Hoar Frost is the Gaseous Water which exists in the Atmosphere, condensed and converted into Ice Crystals. In the winter-time you often notice, on a clear sharp night, that the tops of the houses and the trees are covered with a white powder called hoar frost; and, on the windows of the room when you wake up, you see most beautiful figures, like delicate plants. Take a little of the hoar-frost, or scrape off some of the stuff that makes the window look like ground glass, and you find that it melts in your hand and turns to water. It is in fact ice. And if you look at the figures on the window pane with a magnifying glass you will see that they are made up bits of ice which have a definite shape, and are arranged in a regular pattern. Each of these definitely shaped bits of ice has been formed in the following way. The air in the room is much warmer than that outside, and there is mixed with it nearly as much water, derived from the breath and the evaporation of moist surfaces, as can maintain itself in the gaseous state at the temperature. The windowpanes, being thin, are cooled by the outside air, and of course the gaseous water inside the room, when it comes in contact with the cold windowpanes, becomes condensed on them into fine drops of cold water. The panes becoming colder and colder, these minute drops at last freeze, and the water not only becomes solid, but it crystallises; that is to say, the little solid masses take on more or less regular geometrical forms with flat faces, inclined to one another at constant angles, so that they resemble bits of glass cut according to particular fixed patterns. All ice is in fact crystalline, but in ice which has been formed from thick sheets of water, the crystals are so packed together that they cannot be distinguished separately.
- 29. 43. When Ice is warmed it begins to change back into Water as soon as the Temperature reaches 32°. A lump of ice brought out of the open air in very cold weather may have a temperature of 30°, or 20°, or lower. If such a lump is brought into a warm room it gradually becomes warmer, but remains unchanged otherwise, until it has risen to 32°. Then it begins to melt, and remains at 32° as long as it is melting; and the water which proceeds from it is at first also at 32°. If you were to throw a lump of ice into the middle of a hot fire, so long as a particle of ice remained as such, it would have a temperature of 32° and no more. This is a fact exactly parallel to that which is observed when water is raised to the boiling-point. So long as any of the water remains unconverted into steam it becomes no hotter. Moreover the steam itself is at first at 212°.
- 30. 44. Ice the solid, Water the liquid, and Steam the gas, are three states of one natural object; the Condition of each State being a certain Amount of Heat. Ice, liquid water, and steam, are three things as unlike as any three things can well be. What do we mean then by saying that they are states of one substance, water? What we really mean is that if we take a given quantity of water, say a cubic inch, and change it first into ice and then into steam, there is something which remains identically the same through all these changes. This something is, in the first place, the weight of the material substance. The water weighs 252½ grains, the ice into which it is converted weighs 252½ grains, and the steam produced from it weighs 252½ grains. In the second place, the same force would cause the ice, the water, and the steam, to move with the same rapidity; and, when set in motion, they would produce the same effect upon anything movable against which they struck. In the third place, when you study chemistry, you will learn that the ice, the steam, and the liquid water, would yield the same weight of the same two gases, oxygen and hydrogen, and nothing else. Every one cubic inch of water, 1,700 cubic inches of steam, and 1 111 cubic inch of ice, yield 28 1 18 grains of hydrogen, with 224 8 18 grains of oxygen, and nothing else. (See § 50.) As there is not the slightest difference in weight between a given quantity of water and the ice, or the steam, into which it may be converted, it is clear that the heat which is added to or taken from the water to give rise to these several states, can possess no weight. If then heat is a material body, it must be devoid of weight—and hence, in former times, heat was called an imponderable substance. It was thought to be a kind of fluid, called caloric, which had no weight, and which drove the particles of bodies asunder, when it
- 31. entered them as they were heated, and let them come together as it left and they grew cool.
- 32. 45. The Phenomena of Heat are the Effects of a rapid Motion of the Particles of Matter. This much, however, is certain: that heat can be caused by motion. Every boy knows that a metal button may be made quite hot by rubbing it. A skilful smith will hammer a piece of iron red hot. The axles of wheels become red hot by rubbing against their bearings, if they are not properly lubricated; and even two pieces of ice may be melted by the heat evolved when they are rubbed together. And there are abundant other reasons, as you will find when you study physics, for the belief that the sensation we call heat, and all the phenomena which we ascribe to heat, are the effects of the rapid motion of matter. However, a quiescent body may be made hot without exhibiting the least appearance of motion. The surface of the water in a tumbler at 100° is just as unruffled as that of the same water at 32°. What, then, is meant by saying that heat is a kind of motion, and that the greater the heat in any body the greater the amount of motion in that body? The answer to this question is that the motion which causes the phenomena of heat, is not a visible motion of the whole mass of the hot body, but a motion of the individual particles of which it is composed. And each particle moves, not straight forward, but backwards and forwards in the same space, so that its motion may be roughly compared to that of a pendulum, or to that of the balance- wheel of a watch. It is in fact a sort of vibratory movement; each vibration taking place through a very short distance and with extreme rapidity. The sensation of heat is caused by the vibratory movements of the particles of matter, just as sound is so caused. The prongs of a tuning-fork which has been struck, certainly vibrate, for you can see them do so if the note is low. If you now put your ear at one end of a long piece of timber and the handle of the vibrating tuning-fork is placed upon the other end, the vibratory motion of the tuning-fork will be communicated to the particles of the wood and will be loudly heard. All the time the sound is heard the particles of
- 33. the wood are vibrating. Nevertheless, the wood as a whole does not move, but its particles swing backwards and forwards through such a minute space that their motion is imperceptible. But what are these particles of matter which by their vibration give rise to the phenomena of heat?
- 34. 46. The Structure of Water. We have seen that pure water is perfectly clear and transparent. The naked eye can discern no difference between one part and another. In other words, it has no visible texture or structure. It does not follow that it really possesses none, however, for there are many things which seem to be the same throughout, or homogeneous, which yet show structure if they are examined with a magnifying glass. Thus the surface of a sheet of fine white paper looks perfectly even and smooth to the eye; but a magnifying glass of no great power will show the minute woody fibres of which it is made up; while, under a powerful microscope, the paper looks like a coarse matting. But if we put a small drop of water on a slide, such as is used for microscopic objects, and cover it over with a thin glass so as to spread it out into a film, perhaps not more than 1 10000 th of an inch thick, it may be examined with the very highest magnifying powers we can command, and yet it looks as completely homogeneous and shows as little evidence of being made up of separate parts as before. However, this is still no proof that the water is not made up of little parts, or particles, distinctly separated from one another. It may merely mean that the particles are so extremely small that they cannot be distinguished even by microscopes which magnify four or five thousand diameters. It is certain that solid bodies may be divided into particles so minute that the best microscopes show no trace of them. Common gum-mastic cannot be dissolved by water, but it readily dissolves in strong spirit or alcohol, and mastic varnish is an alcoholic solution of gum-mastic. If you add water to mastic varnish, the alcohol takes away the water and the mastic falls out, or precipitates, as a curdy solid composed of very visible whitish particles. But if a drop of the varnish is added to a good deal, say half a pint, of water and well stirred at the same time, the mastic, though it is still precipitated as a solid, is in a state of extremely minute division. No separate solid
- 35. particles of mastic are visible to the naked eye, but the water assumes a faint milky tinge. This milkiness arises from the presence of solid particles of mastic diffused through the water; and yet, if the experiment has been properly managed, a drop of the fluid may be spread out as before and examined with the highest magnifying powers, and nothing can be seen of such particles. So far as vision goes it might be a drop of pure water. Now our best microscopes are able to show us anything solid which has a diameter of 1 100000 th of an inch, quite distinctly; and probably solid opaque particles of much smaller size would make themselves apparent as a turbidity or cloudiness. The particles of mastic must be therefore so much smaller than this that they remain invisible. Hence it follows that if water were made up of separate particles, or droplets, 1 1000000 th of an inch in diameter, and thus had the structure of a mass of very fine shot, no microscope that has yet been constructed would enable us to see even a trace of that structure. We could not obtain any direct evidence of it.
- 36. 47. Suppositions or Hypotheses; their Uses and their Value. When our means of observation of any natural fact fail to carry us beyond a certain point, it is perfectly legitimate, and often extremely useful, to make a supposition as to what we should see, if we could carry direct observation a step further. A supposition of this kind is what is called a hypothesis, and the value of any hypothesis depends upon the extent to which reasoning upon the assumption that it is true, enables us to explain or account for the phenomena with which it is concerned. Thus, if a person is standing close behind you, and you suddenly feel a blow on your back, you have no direct evidence of the cause of the blow; and if you two were alone, you could not possibly obtain any; but you immediately suppose that this person has struck you. Now that is a hypothesis, and it is a legitimate hypothesis, first, because it explains the fact; and, secondly, because no other explanation is probable; probable meaning in accordance with the ordinary course of nature. If your companion declared that you fancied you felt a blow, or that some invisible spirit struck you, you would probably decline to accept his explanation of the fact. You would say that both the hypotheses by which he professed to explain the phenomenon were extremely improbable; or in other words, that in the ordinary course of nature fancies of this kind do not occur, nor spirits strike blows. In fact, his hypotheses would be illegitimate, and yours would be legitimate; and, in all probability, you would act upon your own. In daily life, nine-tenths of our actions are based upon suppositions or hypotheses, and our success or failure in practical affairs depends upon the legitimacy of these hypotheses. You believe a man on the hypothesis that he is always truthful; you give him pecuniary credit on the hypothesis that he is solvent. Thus, everybody invents, and, indeed, is compelled to invent, hypotheses in order to account for phenomena of the cause of which he has no direct evidence; and they are just as legitimate and necessary in science as in common life. Only the scientific reasoner
- 37. must be careful to remember that which is sometimes forgotten in daily life, that a hypothesis must be regarded as a means and not as an end; that we may cherish it so long as it helps us to explain the order of nature; but that we are bound to throw it away without hesitation as soon as it is shown to be inconsistent with any part of that order.
- 38. 48. The Hypothesis that Water is composed of Separate Particles (Molecules). It has been pointed out that we cannot see, and indeed that there is not much hope of our ever being able to see, the separate particles of water, even if water is composed of such particles. But it is perfectly legitimate to suppose that water is made up of such particles, if that hypothesis will enable us to explain the properties of water. Let us suppose then that any portion of fluid water is really composed of a prodigious number of particles less (and probably much less) than a millionth of an inch in diameter. We may call these particles molecules.[4] 4. Diminutive of moles, a mass. We are justified, in accordance with the general properties of matter (§ 18), in supposing that these molecules tend to approach one another. But the fact that water is slightly compressible justifies the supposition that its molecules are not in actual contact, but that they are separated by interspaces, just as the motes in the air of a dusty room are so separated. What is it that keeps the molecules apart? We have seen that great mechanical pressure brings them but slightly nearer to one another; hence there is an equivalent resistance of some kind which keeps them apart. This resistance must have the same origin as the sensation which we know as heat, for it has been seen that diminution of heat diminishes the bulk of water; that is, allows the molecules to come closer together; that is, diminishes their tendency to keep asunder. Increase of heat, on the other hand, increases the volume of water; that is to say, drives the molecules further apart, or increases their tendency to keep asunder. Suppose we call the cause of the tendency of the molecules of water to come together an attractive force; and the cause of their keeping apart, which manifests itself to us as the sensation of heat and is, as we have seen, in all probability, a rapid vibratory or whirling motion of the molecules, a repulsive force; then, in the
- 39. liquid state, these forces are so adjusted that the molecules are quite free to move, and yet hold together. By adding heat the repulsive force is increased, until the molecules are about twelve times as far apart as they were in each direction; while the attractive force is overcome, and the molecules fly off in all directions as soon as they are unconfined. On the other hand, by taking heat away, the repulsive force is diminished, until the molecules become inseparable and the water assumes the solid form. It is probable that the expansion of fluid water, at a temperature below 39°, depends upon the molecules taking up a peculiar arrangement as they approach one another. If sixteen men are formed into a column, four deep, and each man a foot from the other, the same men may stand closer together and yet form a hollow square, which occupies a larger space. That the molecules of water do take up a particular order in assuming the solid condition, is shown by the crystalline form of ice. Each crystal of hoar-frost owes its shape to the arrangement of its molecules, according to a definite geometrical pattern. Thus the hypothesis that water is composed of separate molecules, is useful, for it helps us to some extent to explain the properties of water. And, when you study physics and learn the laws of motion, you will find that there is no end to the number of the truths established by observation and experiment, which can be explained by this hypothesis. Hence it may fairly be adopted and employed as a means of picturing to ourselves the order of nature, so long as no facts are discovered which are inconsistent with it.
- 40. 49. All Matter is probably made up either of Molecules or of Atoms. The same reasons which lead to the adoption of the hypothesis that water is composed of separate particles justify its extension to all forms of matter whatever. The metal mercury or quicksilver, for instance, may be supposed to be made up of distinct particles of mercury of extreme minuteness, and according to the temperature, these associate themselves in the solid (frozen mercury), liquid (ordinary quicksilver), or gaseous form (vapour of mercury). To whatever treatment pure mercury may be subjected, we cannot get anything but mercury out of it. The particles of mercury have never been broken up. Hence they are generally termed atoms, or particles that cannot be divided; and mercury is said to be an element, or a substance which is not compounded of any other substances. Here is a case in which it is very useful to distinguish between fact and hypothesis. The matter of fact is that, up to the present time, no one has been able to get out of pure mercury anything but pure mercury. The statement that mercury is a simple substance, and therefore never can be broken up into any other substances, is a hypothesis which future observation and experiment may or may not confirm. A hundred and fifty years ago it was universally believed that water was as much an element as mercury. But water is now well known to be a compound. In fact, as has already been said, the particles of water may be very readily broken up or decomposed (in what way, you will learn when you study chemistry) into two totally distinct substances, oxygen and hydrogen, which are gaseous at all known temperatures, though by combining vast pressure with extreme cold they have recently been liquefied. Each of these gases, according to our hypothesis, consists of particles, and since these can by no known means be further broken up, they are considered to be atoms like those of mercury.
- 41. Nine parts by weight of pure water always yield eight of oxygen and one of hydrogen. The hypothetical particle, or molecule of water, therefore, must be composed of atoms of oxygen and hydrogen having this relative weight; and chemists have grounds for believing that one atom of oxygen and two atoms of hydrogen exist in each molecule of water. If this be so, the structure of water must be more complicated than we thought at first; and each particle of water (the molecule) must be a system composed of three separate atoms.
- 42. 50. Elementary Bodies are neither destroyed nor is their Quantity increased in Nature. It has been seen that when a cubic inch of water is dissipated by heat, it is not destroyed, but that it merely changes its form from the fluid to the gaseous state, while its weight remains unaltered. If the same cubic inch of water is decomposed into oxygen and hydrogen gases, the water is indeed destroyed, but the matter of which it consisted remains unchanged in weight. If the water weighed 252·5 grains, the oxygen gas will weigh 224·45 grains and the hydrogen gas will weigh 28·05 grains. And nothing that man has been able to do has affected the weight of a given quantity of either of these gases. So far as we know, elementary bodies retain their weight under all circumstances, and can be traced by it whatever shape they may take. If this is true it follows that, in the order of nature, matter is indestructible: the quantity of it neither increases nor diminishes. Hence it follows that natural things and artificial things resemble one another in one respect. It is true of both that the matter of which they are composed is never destroyed and never increased; and therefore the order of events in nature as much consists in the joining together and putting apart of natural bodies by natural agencies, as the order of events in the artificial world consists in the joining together and the putting apart of natural bodies by human agencies.
- 43. 51. Simple Mixture. In order to learn the manner in which water may be broken up into its elements or decomposed, you must turn to the Primer on Chemistry. But as a preliminary to the study of that science, it may be useful to consider some simple cases of composition and decomposition which are exemplified by water. If half a pint of water, coloured by putting a little ink into it, is added to the same quantity of clean water, the two will readily mingle; the total quantity of water will be a pint; and its colour will be just half as dark as that of the coloured half-pint. This is a case of simple mixture. The volume of the mixture equals the sum of the volumes of the things mixed, and there is no change in the properties of these things. So when water evaporates, the gaseous water or vapour mixes with the air in the same way, the molecules of the one body dispersing themselves between the molecules of the other until there is the same proportion of each everywhere. In like manner, sand and sugar may be (and unfortunately often are) mixed, without any change in the properties of either, or in the space which they primitively occupied. On the other hand, oil and water will not mix, however much you may stir the two together; and the oil, being the lighter, rises to the top as soon as the fluid is quiet. Nor will quicksilver and water mix, but the quicksilver, being very much heavier than the water, rushes to the bottom of the vessel into which the two are put. Neither will sand nor iron filings mix with water; as heavier bodies, they also sink to the bottom. Nor does powdered ice, though it is water in another shape, mix with ice cold water; as a lighter body it floats at the top.
- 44. 52. Mixture followed by Increase of Density; Alcohol and Water. Strong spirit, or alcohol, is a clear transparent fluid which looks like water, but is a very different substance. For example, it boils at a much lower temperature, it burns with a blue flame, it has intoxicating properties, and, like oil, it is very much lighter than water. Hence, if coloured spirit is poured gently upon the surface of water the spirit rests upon the water. Suppose, now, that we take a tall measure graduated into ten equal parts. Fill the lower five with water, and then, very gently, pour in the strongest alcohol, coloured in some way, until the tenth mark is reached. We shall have five volumes of water below, and an equal quantity, or five volumes, of coloured alcohol above. Where the two are in contact, the colour will be diffused into the water for a short distance, but not far, showing that only a slight mixture is taking place. This, however, is not because the two fluids mingle with difficulty; for, with slight stirring, they mix completely, and you have a fluid the colour of which is about half as intense as that of the alcohol, and many of the other properties of which are intermediate between those of pure alcohol and those of pure water. Thus far, nothing further than simple mixture, as when coloured water was added to pure water, seems to have occurred; but, in reality, something more has happened. In the first place, the mixture is a good deal warmer than either of its components; that is to say, heat has been generated. In the second place, if you measure the volume of the whole fluid after it has cooled, it no longer stands at the mark ten, but distinctly lower, or about nine and three- quarters. As the volume of the mixture is less than the sum of the volumes of its two components, it follows that the density of the mixture must be greater than a density midway between that of the water and that of the alcohol. In other words, the molecules in the mixture do not occupy the same space as they did when they were separate. The result is the same as if the ten volumes had been compressed until they occupied only nine and three-quarters; so that
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