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That phenomenon strongly impressed on him the conviction, that 

 something existed at the surface of the sun which intercepted his 

 light, more at certain points than at others ; and he conceived that 

 the matter composing the red prominences, might he the absorbent 

 medium which produced that effect. 



2. On a Universal Tendency in Nature to the Dissipation 

 of Mechanical Energy. By Professor William Thomson. ' 



The object of the present communication is to call attention to 

 the remarkable consequences which follow from Carnot's proposition, 

 established as it is on a new foundation, in the dynamical theory of 

 heat ; that there is an absolute waste of mechanical energy available to 

 man, when heat is allowed to pass from one body to another at a lower 

 temperature, by any means not fulfilling his criterion of a " per- 

 fect thermo-dynamic engine." As it is most certain that Creative 

 Power alone can either call into existence or annihilate mechanical 

 energy, the " waste" referred to cannot be annihilation, but must be 

 some transformation of energy.* To explain the nature of this 

 transformation, it is convenient, in the first place, to divide stores 

 of mechanical energy into two classes — statical and dynamical. A 

 quantity of weights at a height, ready to descend and do work when 

 wanted, an electrified body, a quantity of fuel, contain stores of 

 mechanical energy of the statical kind. Masses of matter in motion, 

 a volume of space through which undulations of light or radiant heat 

 are passing, a body having thermal motions among its particles 

 (that is, not infinitely cold), contain stores of mechanical energy of 

 the dynamical kind. 



The following propositions are laid down regarding the dissipation 

 of mechanical energy from a given store, and the restoration of it to 

 its primitive condition. They are necessary consequences of the 

 axiom, ^' It is impossible, by means of inanimate material agency, 

 to derive mechanical effect from any portion of matter by cooling 

 it below the temperature of the coldest of the surrounding objects.''^ 

 {Dynam. Th. of Heat, % 12.) 



I. When heat is created by a reversible process, (so that the 

 mechanical energy thus spent may be restored to its primitive con- 



* See the Author's previous paper on the Dynamical Theory of Heat, § 22. 



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