Mechanical 'Energy of the Universe. 99 



Professor William Thomson of Glasgow, on the tendency 

 which exists in nature to the dissipation or indefinite diffu- 

 sion of the mechanical energy originally collected in stores 

 of power. 



The experimental evidence is every day accumulating of a 

 law which has long been conjectured to exist, — that all the dif- 

 ferent kinds of physical energy in 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, magnetism, electricity, or chemical agency, or 

 in other forms not yet understood, is unchangeably the trans- 

 formations of its different portions from one of those forms 

 of power into another, and their transference from one por- 

 tion of matter to another, constituting the phenomena which 

 are the objects of experimental physics. 



Professor William Thomson has pointed out the fact, that 

 there exists (at least in the present state of the known world) 

 a predominating tendency to the conversion of all the other 

 forms of physical energy into heat, and to the uniform diffu- 

 sion 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 currents, part only of which 

 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 con- 

 verted into visible motion, or into a store of visible mechani- 

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

 elastic 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 pro- 

 portion only of the heat, depending upon the range of tem- 

 perature through which the elastic body works, can be con- 

 verted, 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. 



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