514 PRESENT FUNDAMENTAL CONCEPTIONS OF PHYSICS. 



contrary to the design of their inventors, heat their surroundings, and 

 it is only by making a virtue of necessity that this can be turned to the 

 best advantage. The heat expended in this involuntary heating pro- 

 cess, added to that expended in useful mechanical work, gives the total of 

 heat which the medium (vapors or gases) had received from the higher tem- 

 perature of the heat source. If the work performed be measured and a 

 careful calculation of all the losses of heat made, it follows that the 

 work done by the machine is the exact equivalent of the apparently [or 

 rather actually] lost amount of heat.* 



It is not only in thermo-dynamic machines, but in all conversion of 

 heat into work (as both practice and theory teach us), that it may be 

 said that but a small part of the "descending " heat, that is heat pass- 

 ing from the warmer to the colder body, can be transformed into useful 

 work, for the greater portion of the heat passes directly as such to the 

 colder body. Clausius has however demonstrated (1850) that heat 

 can only pass over or " ascend" from a colder to a warmer body when 

 for the raising of the temperature, work is expended. This proposition 

 has the result that the last hope of the enthusiasts for a "perpetual 

 motion " is entombed. Their hope was based on the possibility that 

 the heat, which is produced in machines by impediments of motion — fric- 

 tion, shocks, resistance of the medium — might be reconverted into work, 

 and at least a mechanism might be constructed which would be perma- 

 nently automatic. In this, one thing was forgotten, that heat can never 

 be entirely converted into work, but that on the contrary only the 

 smaller portion of the higher temperature from the source of heat can 

 be thus transformed, and that the greater part of it in passing to bodies 

 of lower temperature must ever remain as heat. The perpetuum mobile 

 therefore remains impossible. 



By means of the theory of the conservation of energy the impossi- 

 bility of a perpetual motion has been finally proved : for what is the 

 result of that theory ? Work can only be performed by an energy em- 

 ployed for the purpose ; if the latter is exhausted or transformed it can 

 perform no further work. It can no longer be assumed that perhaps 

 by means of the thermal, electrical, or magnetic forces the construction 



* Clausius has suggested the employment of the term ergon to express the numerical 

 value of the work-unit when measured by the heat-unit. And he further proposes an 

 adjective form of this word (crgonized) as a substitute for the manifestly inaccurate 

 term " latent" when applied to heat. As he well remarks: "This name originated 

 when it Avas thought that the heat which can no longer be detected by our senses 

 (when a body fuses or evaporates) still exists in the body in a peculiar concealed con- 

 dition. According to the mechanical theory of heat, this notion is no longer tenable. 

 All heat actually present iu a body is sensible heat : the heat which disappears dur- 

 ing fusion or evaporation is converted into xvork, and consequently exists no longer as 

 heat. I propose, therefore, in place of latent heat to substitute the term crgonized heat." 

 {The Mechanical Theory of Heat. Edited by Prof. T. A. Hirst. 8vo. London. 18G7. 

 Sixth Memoir. Appendix A. pp. 253,255.) This collection of memoirs, by Prof. R. 

 Clausius, originally appeared in Poggendorll's Annalen, and they were translated from 

 the German for the L. E. D. Philosophical Magazine, by Prof. J. Tyndall and others. 



