the Foundations of Dynamics. 29 



will then be abundance of motion but no force, and therefore 

 no " activity." 



To make use of the readily detachable portion of energy 

 may not be a very simple thing, and commonly requires a 

 machine, sometimes an ingenious machine. Give a savage 

 a charged Ley den jar, and he will probably detach from it its 

 available energy pretty soon. But give him a charged 

 storage-battery and he will not know what to do. A bit of thin 

 wire, however, is all the mechanism absolutely needed in order 

 to afford him some light and heat ; if mechanical motion is 

 required then some form of dynamo or electromagnetic 

 motor must be supplied. Often and often we do not know 

 how fairly to utilise even the portion of energy automatically 

 streaming off from a body — from a gas-flame for instance 

 when we need light. To utilise more of a body's energy 

 than it will part with is impossible ; but the progress of 

 science may conceivably teach us, not only how to utilise the 

 whole of what bodies already freely give off, but also perhaps 

 even how to make bodies (say molecules for instance) part 

 with much energy which at present, if left to themselves, they 

 permanently retain. 



The first and most general portion of the second law of 

 Thermodynamics, stated above in italics, will always remain 

 true, even when the second part, about the non-uphill flow 

 of heat, has by future discovery been upset ; because the 

 application of a machine for the purpose of extracting other- 

 wise retained energy, not by a process analogous to pumping 

 but by enabling it automatically to flow whereas without the 

 machine it could not, can hardly be regarded as other than 

 automatic ; else would the present machines for directing the 

 flow of already available heat be liable to a similar objection. 

 Even if the contrivance necessary for extracting molecular 

 energy turn out to be a live thing, — and this Dr. Johnstone 

 Stoney* most suggestively conceives it possible may be 

 the function of some bacteria [a remarkably appropriate de- 

 moniacal function for the producers of disease] , yet life, too, 

 so far as it falls into the scheme of physics, must be con- 

 sidered as an automatic process, and only the energy which by 

 any device a body can be made automatically to yield without 

 pumping can ever be utilised. But statements about heat 

 not flowing up hill, or about not cooling bodies below 



-pp = 0, or dQ = Td<j>, &c. ; 



these are liable to ultimate modification with the progress of 

 science, since the very terms Heat and Temperature are 



* Phil. Mag. April 1893. 



