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Show Fireside Science , By Rjuuotna Sutton Caarrlskt, 1111 4N. T. veals-WihII, veals-WihII, frees raala-siaa C. . IVEHYOAY PMYgICa MAT. Rven a slight knowledge of physics will enable one to understand many of the wonderful forces at work la our bomee end gsrdens. Heat comes first. It warms us, cooka our food, malntalna the svan temperature or our bodiea close to 11.4 degreee. end makea the flora af tha whole earth grow. Heat la produced by molecular mo- tlon a statement saslly underetood by persona famllar wtlh the oompti- sltlon of matter. A basin of water, , like all other forma of matter, wheth- a er llauld. solid or gaseous, would look 1 Ilka a baeln filled with allppery, little, I three. In-ona aaota. provided a auffl- I clently powerful aaloroscop could bs I focused upon It. To each atom of I osygea.two atom f hydrogen would I be attached, the three atoms together I forming a water molecule. Between I the molecules, open spaces relatively I as large aa the opaa apaeee la a baa- -kat of apple would ba aeen. In tkeae apacea dlaeolved augar rilaairpaafB Inataad of lying Inert, the mole- culea ar In ceaaelaaa agtlatlon. By . heating th basin tha asitatoln X among the moleculea Increases. If asfflcantly heated, the water bolla, which maane that the anolec-ulee are la violent agitation. Sa great Is tha satiation that the surface moleculea beain flying off Into space as steam. it will now bs undsrstood why heat causae substance to expend. When ' turned Into steam, water occupies 100 time aa muck apace as whea liquid. Aa water la a teapot beats It expande and raises ths lid. Ths sxpanalve power of steam pushes ths plstou of the locomotive back and forth, cooling, cool-ing, on ths other band, elowa down molecular motion aad causes aub-etancee aub-etancee to contract. The gap between be-tween ateel ralla, oa a railroad, ara wider la the summer than during the winter, dus to the huddling together of the steal molecules caused by cold. To raise ths temporal urs of a body, therefore, we heat It. which la another way of saying that, aa a body warme. it takes la beat; aa It cools. It gives off heat. If you take a stick and agitata the water la a pool, you will see wavee epread away from th atlok; Hence, an aaltatlon started at any one point, apraada throughout the pool. In like manner, an agltatloa among the moleculea mole-culea of a eubetance producea wavea In the ether, eurroundlna rhe molecules, mole-cules, and the agitation spreads more n. 1Mb nMlv i.inriln. knni Ikk "heat conduct ivlty'r of th aubstanco. Just as a vibrating tuning fork, or violin suing, producea sound wave In th air, vibrating molecules produce heat 'wave nl tha ether permeating a vary substance. Aa a. substance cools, tha vibration vibra-tion among the molecule low down and a s.lm comas. In th cooling pro- f cess, when ths substance has given I off all its heat: then tha vibrations J ceaae. the molecule II Inert. Ilk ap- ' plea In a basket, which means that tna substance can get no colder. If a thermometer can be invented which would not Itself frees up. It would sink lower and lower, as a substanc cools, nntll 17t degrees below be-low aero (absoluto sero Centlgradel wer reached, when It would stand still. .Nothing can b colder than that for. without aom movement among th moteoulus. heat wavea in th aur- . rounding ther could not b pro- M 1 ducod. Degre by degree, as gasea M cool, they shrink ar contract. l-17.d w In volum. and at abooiut sero disappear. dis-appear. What becomes af them la aot known. |