494 



HEAT. 



magnetic effects ; and also of forming and de- 

 composing chemical compounds. 



But investigation has gone still further. It 

 is found that all these changes take place in 

 rigorous accordance with the laws of quan- 

 tity. As matter cannot be destroyed, neither 

 is force capable of destruction ; and as mat- 

 ter may be pursued through all its multitu- 

 dinous changes without loss, the same prin- 

 ciple is found to hold in regard to force. 

 It has long been familiarly known that ma- 

 chines do not create force, but only commu- 

 nicate, distribute, and apply that which is im- 

 parted to them. In all cases the force expend- 

 ed is exactly measured by the resistance over- 

 come. In the case of water-power, to lift a 

 hammer of 100 pounds one foot high at least 

 100 pounds of water must fall through one 

 foot; or, what is the same thing, 200 pounds 

 must fall through half a foot, or 50 pounds 

 through two feet. If a hammer weighing 

 1,000 pounds is employed with the same driv- 

 ing force, it will either be raised to only one- 

 tenth the height, or, tenfold the time will be 

 required to raise it the same height. Thus in 

 machines a certain amount of power acting as 

 cause, produces an exactly equal amount of 

 change, as effect. 



ft is precisely the same when the molecular 

 forces are involved those forces which involve 

 the agency of atoms. It is well understood 

 that a certain amount of fuel is necessary to 

 perform a given amount of work with a steam 

 engine. This means, strictly, that definite 

 quantities of the chemical action of combustion 

 give rise to a fixed quantity of heat, and this 

 to a determinate quantity of mechanical effect. 

 Dr. Faraday made the important discovery of 

 the definite chemical effect of the voltaic cur- 

 rent. He found that an equivalent of an ele- 

 ment consumed in a battery gives rise to a 

 definite quantity of electricity which will pro- 

 duce exactly an equivalent of chemical decom- 

 position. For example, the consumption of 32 

 grams of zinc in the battery excites a current 

 which will set free from combination 1 grain 

 of hydrogen, 104 of lead, 108 of silver, 39 of 

 potassium, and 31 '6 of copper. But these are 

 the combining numbers of those elements, and 

 thus is established a remarkable equivalency 

 between chemical and electrical forces. 



That a certain amount of heat produces a 

 definite quantity of mechanical force has been 

 long known ; but only lately has the question 

 been inverted : how much heat is produced by 

 a certain amount of mechanical force? The 

 answer to this question gives rise to the science 

 of thermodynamics. All friction, collision, 

 and condensation, whether of solids, fluids, or 

 gases, produce heat. But to ascertain at what 

 rate mechanical force produces heat it requires 

 certain standards of comparison known as the 

 units of heat and force. The English unit of 

 heat is one pound of water, raised through 1 F. 

 The unit of force is one avoirdupois pound 

 falling through one foot of space. By a great 



number of experiments, Dr. Joule of Manches- 

 ter, Eng., demonstrated the mechanical equiv- 

 alent of heat that is, how many units of force 

 are equal to a unit of heat. He agitated water, 

 mercury, and oil successively in suitable ves- 

 sels, by means of paddles driven by falling 

 weights, and determined the exact amount of 

 heat produced, and the force spent. By varied 

 and repeated operations, conducted with con- 

 summate skill and great patience, he found that 

 the same expenditure of power produced the 

 same absolute amount of heat, whatever ma- 

 terials were used ; and that a pound weight 

 falling through 1 foot, and then arrested, would 

 produce a unit of heat, that is sufficient to raise 

 1 Ib. of water 1 F. The vast significance of 

 this fact to science is obvious; every move- 

 ment that takes place throughout the universe, 

 whether of molecules or masses, has its fixed 

 thermal value it represents and may be con- 

 verted into a definite amount of heat. 



The imponderables, then, have passed away, 

 with the epicycles of the old astronomers and 

 the phlogiston of the old alchemists monu- 

 ments of the past progress of thought and we 

 have in their stead pure forces which are all 

 varying modes of motion of ordinary matter. 

 Science assumes the atomic constitution of 

 matter ; that there are interspaces between the 

 atoms, and that these atoms are capable of va- 

 rious motions, and are probably in a state of 

 constant movement. They may rapidly oscil- 

 late backward and forward, or whirl upon 

 their axes, or even revolve through orbits, like 

 what we may term the larger atoms of the 

 solar system. Perhaps they execute several of 

 these movements at the same time as do the 

 planets. They are also believed to be endowed 

 with polarities, and that their motions are sub- 

 ject to a polar control. Each molecular force 

 is regarded as a mode of motion among the 

 atoms; and as these motions may pass into 

 each other the forces are convertible. Heat is 

 that mode of motion among atoms by which 

 they are caused to move further apart, pro- 

 ducing expansion of the mass, or heating it. 

 As the motion declines the body contracts and 

 cools. Heat is produced by friction or collision 

 because the mechanical motion which is arrest- 

 ed and disappears is changed to the molecular 

 motion of the mass ; while the mechanical mo- 

 tion produced by heat, as in the case of tho 

 steam-engine, is simply the consequence of tho 

 translation of atomic movement into massivo 

 motion. No force can be annihilated, and 

 what the atoms lose, the mass gains. 



Caloric, the electric fluid, and luminous cor 

 puscles are denied ; yet science still holds to tho 

 conception of a universal ether. Some writers, 

 prominent among whom is Mr. Grove, protest 

 against this as an inadmissible assumption. 

 They say we can neither make nor prove tho 

 existence of a perfect vacuum, and, therefore, 

 are not entitled to deny that matter is univer- 

 sal. There may be, and there probably ia, 

 matter, hi some form, however attenuated, 



