PRESENT FUNDAMENTAL CONCEPTIONS OF PHYSICS. 513 



and lastly into mechanical motion, which may be employed in the per- 

 forming of mechanical work. 



For every amount of work done by the electric current an equivalent 

 of the energy of the current, or of the combustion heat of the oxidizing 

 zinc in the battery, is consumed or rather transformed. We have seen 

 that in the steam-engine a part of the heat of the steam is turned into 

 mechanical work, and that after the work is accomplished this amount 

 of heat is wanting in the steam that has been at work. In steam- 

 engines, and in fact in all caloric or thermo-dynamic machines, a pro- 

 portionate quantity of the heat, stored up in the form of vapors and 

 gases, must seemingly disappear for every mechanical work done by 

 such machine. Heat is only then turned into work if it passes from a 

 warmer to a colder body; in this respect it resembles the flow of water 

 (as Sadi Carnot ingeniously remarked as early as 1824), which only then 

 can move mills and perforin other work when it is able to descend from a 

 higher to a lower level. This figurative conception, however, led Carnot 

 to the false conclusion that in this sinking of heat from the higher to 

 the lower tempered body no heat was lost. Ultimately Clausius cor- 

 rected Carnot's proposition of the performance of work by the falling 

 of temperature (18,50), by changing the closing part of Carnot's propo- 

 sition of the retention of heat to the exact opposite, that is, he concluded 

 that there is an apparent loss of a proportionate amount of heat as such 

 for every unit of work done, on account of its transformation into 

 work. Clausius demonstrated furthermore, in agreement with Carnot 

 that in any thermodynamic machine it was to be presumed that the 

 work performed depended in each case on the amount of transmitted 

 heat, and not on the material composition of the vehicle of heat, as for 

 example, whether from steam or heated gas. 



A steam or gas machine can only then perform work when the heat- 

 bearing medium is cooled off on one side of the piston and a part of the 

 heat is converted into work.* 



In every thermo-dynamic machine a warmer body (the fire) transmits 

 a certain amount of heat to the heat bearer (vapors or gases). The lat- 

 ter effects the transformation of the smaller portion of the received heat 

 into mechanical work", while the supplementary, larger portion, is carried 

 over to the colder body. Thermodynamic machines unavoidably, and 



* [This passage correctly recognizes the well-established fact that heat is lust (or de- 

 stroyed) in being 1 ransformed into " work."' Whenever a permanent molecular change 

 is effected either by heat or by impact, less heat remains than when no such work is 

 effected. The falling stone (to use the lecturer's early illustration) is less heated by 

 collision if broken than if not broken by the shock, — a, portion of the kinetic energy 

 in this case being expended in overcoming tin- tenacity of cohesion. Any hypothesis 

 of the conservat ion of motion (as such) would necessarily lead us to the incongruity of 

 conceiving the rolled iron or the crushed ore as having an extra amount of ••latent'' 

 heat stored up within its molecules ; or conversely of conceiving light as "latent" in 

 the gas-holder, the oil-can, or the Inciter match ; or sound as "latent" in the orgau- 

 bellows, the violinist's elbow, or the grain of guupowder. — Ed.~\ 



S. Mis. ot ;;a 



