the Mechanical Energy of the Universe. 359 



The experimental evidence is every clay accumulating, of a lavr 

 which has long been conjectiu-ecl to exist, — that all the different 

 kinds of physical energy iu the universe are mutually convertible, 

 — that the total amount of physical energy, whether in the form 

 of visible motion and mechanical power, or of heat, light, mag- 

 netism, electricity, or chemical agency, or iu other forms not yet 

 understood, is unchangeably the transformations of its different 

 portions from one of those forms of power into another, and their 

 transference from one portion of matter to another, constituting 

 the phenomena which are the objects of experimental physics. 



Professor William Thomson has pointed out the fact, that thei'e 

 exists (at least in the present state of the known world) a predo- 

 minating tendency to the conversion of all the other forms of 

 physical energy into heat, and to the uniform diffusion of all 

 heat throughout all matter. The form in which we generally 

 find energy originally collected, is that of a store of chemical 

 power, consisting of uncombined elements. The combination of 

 these elements produces energy in the form known by the name 

 of electric cm-rents, part only of which can be employed in ana- 

 lysing compounds, and thus reconverted into a store of chemical 

 power ; the remainder is necessarily converted into heat : a part 

 only of this heat can be employed in analysing compounds, or in 

 reproducing electric currents. If the remainder of the heat be 

 employed in expanding an elastic substance, it may be entirely 

 converted into visible motion, or into a store of visible me- 

 chanical power (by raising weights, for example), provided the 

 clastic substance is enabled to expand until its temperature falls 

 to the point which corresponds to absolute privation of heat ; but 

 unless this condition be fulfilled, a certain proportion only of the 

 heat, de])ending upon the range of temperature through which 

 the elastic body works, can be converted, the rest remaining in 

 the state of heat. On the other hand, all visible motion is of 

 necessity ultimately converted entirely into heat by the agency 

 of friction. There is thus, in the present state of the known 

 world, a tendency towards the conversion of all physical energy 

 into the sole form of heat. 



Heat, moreover, tends to diffuse itself uniformly by conduc- 

 tion and radiation, until all matter shall have acquired the same 

 temperature. 



There is, consequently, Professor Thomson concludes, so far 

 as we understand the present condition of the universe, a ten- 

 dency towards a state in which all physical energy will be in the 

 state of heat, and tliat heat so diffused that all matter will be at 

 the same temperature ; so that there will be an end of all i)hy- 

 sical pha,'iiomena. 



Vast as this speculation may scorn, it appears to be soundly 



