Curiosities of Heat

promptly in place

ay take a rapid review of the effects and laws of heat. Wil

ir: com

s combu

with some combustible substance, a

answer cor

r, blushing; "I spok

correct yo

hief effect of h

lities of bodies are not changed: they are not made either heavier or lighter. A sufficiently high temperature renders bodies luminous, and then we call them red hot or white hot. Solid bodies begin to be luminous at a tempe

d are larger in winter than in summer, showing that the rails are shorter in winter than in summer. While skating during the cold winter evenings upon the mill-pond, I have seen cracks in the thick ice start and run across the mill-pond with a roar almost like thunder.

e St. Lawrence at Montreal rises and falls two and one-half inches on account of greater expansion of the upper surface when exposed to the heat of the sun, while a loaded freight train causes a depression of but one-fourth of an inch. A few years since, in order to make some philosophical experiments conn

l raised

is it,

hat the mountain ranges were thrown up by the cont

tions of it molten. It is by very many believed that the whole interior is molten. The crust of the earth may have been formed by cooling. If after an outer crust had been formed, and its temperature had fallen so low as to become nearly stationary, the interior mass continued to cool, the molten mass would tend to sink away from the crust and the crust would sink in upo

nk you have already giv

erred to it, but yo

ion, requires that the atoms of bodies shall not be packed in absolute contact, and the more intense the agitation or the wider the swing

ok now at some of the secondary effects of

powers the cohesive a

ohesive at

t is, bodies like iron or copper or silver, composed of but one kind of substance, o

ns of the effect of heat in o

der heats his metal till its cohesion is so far destroyed that it becomes fluid and can be poured into the mould. Heat relaxes the coh

up Peter: "is it not because heat destroys t

twenty or thirty times its original bulk and the minute starch grains burst open. In cooking potatoes the starch of the potato absorbs a portion of the water that is in it, and thus renders it dry and mealy. The action of heat and water upon rice, wheat, and other grains is similar to their operation upon starch. In the baking of bread the starch is converted into gum. In boiling flesh the effect is partly due to the solv

heat very important both in natu

chemical affinity

tions to assert their strength. But the fact is that, while in many cases the chemical affinities act with great energy at ordinary temperatures, in other cases th

ts are brought into so close contact, yet they do not combine and explode till heat is applied. The same is true of the combustion of wood and coal. The carbon and the hydrogen of the fuel are constantly surrounded with the oxygen of the air, but they do not take fire and burn, that is, they do not combine with the oxygen, till they are raised to a red hea

and air furnish the needed material for the growth of forest trees in winter as well as in summer, but the cold holds in check the chemical forces and prevents the requisite chemical combinations. No sooner does the sun quicken that atomic vibration or revolution which we call heat than vegetable growth begins. Heat is necessary for those chemical changes by which food is digested in the stomach and the processes of nutrition carried on in every part of the body. If a man finish his dinner

expands bodies, weakens cohesive attraction, and

in raised

do you

this weakening of cohesive attraction is e

n, their attraction for each other would be four times less than it now is; if its distance were three times as great, their attraction for each other would be nine times less. The attraction of gravitation diminishes in proportion as the square of the dist

r raised

l you say

n bricks, not to soften

oo great heat will melt bricks while in the process of burning. I once heard a brick-burner say that he could melt the brick around the arches in his kiln in half an hour, if h

er will not burn. Is it because it evaporates be

of the Creator so very important that we will stop to notice it. I think, however, that b

ther substance called a combustible. The rusting of iron an

the compositi

rts of oxygen to one of hydrogen, by weight, or tw

hey mixed together as oxygen and nitrogen are mi

y are burned together. When hydr

ombustion. Can you not now te

he supporter of combustion, will not burn, and the hydrog

burn because it is the production of combustion. A candle is extinguished by it as quickly as by water. By a recent invention carbonic acid is used to extinguish conflagrations.

ill not burn, but will you please also to tell us why

dmitted again before the fuel had cooled down below the burning point, combustion would at once begin again. A blazing brand is extinguished by being thrust into ashes, because it is shut away from oxygen. In the same way we extinguish the flame of a candle with a tin extinguisher. On the other hand, fires often go out because the necessary temperature is not maintained. Water puts out fire in both these ways, but especially by the second. Water poured in torrents f

must look at more carefully in a future lesson. We will suppose that a house is in flames. A fire engine throws a stream of cold water into the midst of the conflagration. The cold water, dashing against the burning wood, cools the heated surface; it is absorbed into the pores of the wood and hinders its rapid heating; a portion of the water, being changed

ish his ends. Heat brings the iron from the native ore, and heat renders it malleable and plastic to be shaped for man's uses. Heat quickens the chemical affinities and renders the arts of civilized life a possibility. Heat brings together oxygen and carbon in ten thousand furnaces, and the heat engendered by the combustion, changed to force, drives the ponderous or nimble machinery which carries on the work of the worl

ished to bless his creatures. I am not much given to moralizing, but when I see how completely these simple effects of heat meet man's wan

hat Prometheus stole fire from Jupiter and brought it down to man in a

there was no need that men should steal fire from the go