486 PRESENT FUNDAMENTAL CONCEPTIONS OF PHYSICS. 



might be destroyed ; now it is known that the visible motion of the 

 fallen stone transforms itself into the invisible one of its molecules by 

 which its temperature is somewhat increased. Light falling on a 

 black cloth, being, so to speak, swallowed up or absorbed by it, was for- 

 merly considered as absolutely extinguished or completely annihilated 

 by it; now it is known that the rays of light are not destroyed thereby 

 but they are transformed into heat. 



Such examples might be indefinitely multiplied, tending to show that 

 an apparently destroyed force can never be lost in reality, but that the 

 effects of these forces are only changes or transformations. By ingenious 

 tests in measurements, these hidden and reappearing actions of natural 

 forces (that is the motions of bodies and their ultimate particles) can be 

 traced ; it can be proved that in nature no part of the action of force — 

 (or of the motion of bodies and their ultimate particles) can ever be 

 lost; and at the same time that no force — no action of force or motion — 

 can ever be created anew ; but that all natural phenomena are the various 

 effects of the original force or existing motion, present in the universe in 

 an invariable quantity. 



If we search for the beginnings of this reformation in the fundamental 

 conceptions of natural science we must, in order to understand them, 

 turn to the theory of heat. It is familiar, that the peculiar condition of 

 bodies by which they produce in us the sensation of warmth and cold, 

 and in other bodies a change of volume, is called their thermal state. 

 We distinguish by our sense of feeling the different degrees of heat of 

 bodies and designate them thereby as hot, warm, tepid, cool, or cold. 

 There are then degrees or grades in the heat of bodies. The definite 

 degree of heat of.a body is called its temperature. To ascertain the 

 temperature of different bodies thermometers are used. These however 

 indicate only the different degrees of heat in a body, but cannot indicate 

 directly the amount of heat contained in it. To do this a particular 

 apparatus is needed which is called a calorimeter. In this, thermo- 

 metrical measurements, of course, are also included, but there are in 

 addition certain calculations necessary to elucidate the amount of heat 

 in question. 



The following is a very simple example of a calorimetrical test, and the 

 calculation referring to it is also annexed ; we thereby arrive at a correct 

 idea of a heat-unit and consequently the possible numerical expression 

 of amounts of heat. On mixing one kilogram (leg.) of water at 0° C. with 

 one leg. of quicksilver at 34° C, the mixture will show 1° C, the water 

 taking 33° C. from the quicksilver, and these raise its own temperature 

 by only 1° C. One leg. of water, then, should have 33 times as much 

 heat supplied to it as one leg. of quicksilver if the temperature of the 

 water is to rise 1° C. This example shows that a thermometer cannot 

 directly indicate what amount of heat is needed to raise the temperature 



