isa-normaladvance-1909-00011

Description:	THE NORMAL ADVANCE11SCIENCE DEPARTMENTExpansion and Contraction Due to Heat and ColdA Russian proverb has it that a certain manwent through a forest and saw no firewood.Likewise do untold thousands of men walkthrough the world and discern not the simplestthings about them, even those objects and processes upon which their very lives depend. Letus take a lay excursion as it were, and goingover into the realm of science study one lawof our great and wise benefactor, Nature,—alaw, some of the facts concerning which everyman knows but the tremendous importance ofwhich only the few ever stop to consider. Irefer to the law: Heat expands, cold contracts.Telegraph wires sag more in summer thanin winter concrete walks are upheaved inwarm weather a stringed instrument tuned ina warm room, rises in pitch when removed to acold one ice floats steam rises from thekettle on the fire,—these are some of the common illustrations with which every one is familiar. To the casual observer they have littlesignificance to the man of science, they arethe expressions of a great law.There have been two theories of expansionadvanced. One may be called the materialtheory, the other the motion theory. Theformer almost carries the meaning in its name.There was a time when men looked upon heatas a material thing—a body, not an energy.They called it phlogiston. It was held thatthe molecules of a body were each surroundedby an atmosphere called caloric. All thephenomena of heat and combustion were attributed to caloric. When a body was heated,the caloric became active and crowded theneighboring molecules with their atmospheresaway. The expansion of the body was due tothe combined effect of all the molecules, thuseach holding the other molecules at armslength as it were.Then came forward other scientists withthe motion theory. Some one had noticedthat the shade of a vibrating tuning-fork appeared larger than the shade of the same forkmotionless. John Tyndall, while on a ship atsea one night was looking at the planet Jupiter.Shifting his position, he again looked at ourhuge neighbor. It seemed much larger nowthan it did before he changed places but italso shone dimmer. The simple explanationwas soon found. The air over the funnel ofthe steamer was between him and Jupiter. Theeffect was the same as if the planet itself weremaking great leaps into space in all directions,and back again at once. Here is the motiontheory of heat: the molecules of a body arenot motionless, but in a continual dance. Whenheated the distance of each molecules motion isincreased, and it therefore uses more space.The other molecules must get out of its way.Tyndalls own words are: When instead of amotionless molecule, we have a vibrating one,we must make room not only for the atomitself, but also for the distance over which themotion reaches. So, today, we say that heatis the energy of molecular motion. Cold is,of course, a negative term, expressing absenceof heat.Matter may be divided into solids and fluids,and fluids into liquids and gases. Hence, weshall have the principle of expansion as dealing with solids, liquids and gases. We take upexpansion of solids first. Some common instances have already been mentioned, but weneed not go far for others. For example, railroad irons, if placed in summer are laid withends in close juxtaposition if laid in winter,a space of a half-inch is left between rails this allows for expansion in summer. One endof iron bridges is often placed upon rollers forthe same reason. Brooklyn Bridge has a telescoping joint in the roadway at the middle of
Source:	http://indstate.contentdm.oclc.org/cdm/ref/collection/isuarchive/id/34041
Collection:	Indiana State University Archives

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