M. F. Mobr on the Nature of Heat. Ill 



of heat are not identical ; their difference has been hitherto 

 just as little cleared up as that between rays of heat from 

 different sources. 



The difficult idea of imponderability is at once got rid of, 

 since a body when vibrating cannot be either heavier or lighter 

 than when at rest. The so-called absolute zero [of tempera- 

 ture] is therefore absolute rest — no doubt altogether unknown 

 to us in reality, but presenting no difficulty to the mind. 



Heat appears as force {Kraft). It overcomes the cohesion 

 of bodies, which is a force ; but that which overcomes a force 

 must be itself a force. And the expansion of bodies by heat is 

 a force-phenomenon of the highest kind ; but that which pro- 

 duces motion or manifestation of force must be a force. 



The expansion of bodies by heat is thus an extended ampli- 

 tude of vibration. The bodies themselves do not expand, but 

 only the space they occupy is increased by their larger vibra- 

 tions. The compression of bodies is due to a change of the 

 amplitude of vibrations by external power. At the absolute 

 zero all bodies must be absolutely incompressible. One can 

 measure the expanding force in certain bodies in terms of 

 weight. Water expands by heating 0*00466 of its volume for 

 1° C. Experiment shows that water loses about too^ooo °f 

 its volume under one atmosphere of pressure. To expand 

 water thus much by heating there would be necessary 



f^tt^tt^k- = 7^ 0. The two forces would then be in equili- 

 0-004660 97 u 



1° 

 brium. Heating by ^= C. produces in water a force of pres- 

 sure of one atmosphere. 1° C. is thus to be considered = 97 

 atmospheres, and 10° C. = 970 atmospheres. 



When a body passes from the solid to the liquid state, heat 

 becomes latent. But one cannot understand how heat can be 

 present in a body without becoming evident to our senses. 

 The usual explanation is that the body is melted ; but this is 

 no explanation, merely the repetition of the fact to be explained. 

 The easier explanation, from our point of view, is as follows : 

 when heat-force is expended in overcoming another force, 

 cohesion, it must itself cease to be perceptible as force ; thus 

 every case in which heat becomes latent is connected with 

 production of motion or with alteration of state of aggregation 

 — that is, with annihilation of material forces. Since matter 

 cannot overcome any force, this explanation was not at the 

 command of the old view. A melted body cannot solidify 

 without giving up to another body the force which destroys its 

 cohesion: — Evolution of heat in the solidification of melted bodies. 



