NOTE A TO PAGE %%. 



Reference to the Views of Roget and Faraday. — 

 " Force" destructible and " Force" indestructible. — Extract 

 from Faraday's "Experimental Researches in Electricity" 



The view that "force " (as Joule both conceived and 

 defined force) is indestructible, to which view Joule was led 

 in 1843, by the discovery of its conversion into an equivalent 

 of heat constituted the final and crowning step in the 

 discovery of the law of the conservation of energy. It was 

 also the step which met with the greatest obstruction from 

 preconceived opinions and the experience associated with 

 what was vaguely known as "force." Joule had generalised 

 " force " to include whatever is now called energy ; but 

 according to the then general use "force " included only that 

 portion of energy, which, in virtue of its condition, could be 

 converted into available effect, which portion of energy, after 

 the reconversion by friction of the effect into heat, having 

 lost its condition of availability, ceased to be "force." Thus, 

 according to the general meaning attached to " force," it 

 was universally and rightly held to be destructible, and the 

 indestructibility of "force" only became true when the 

 conception of "force" had been extended as in Joule's mind. 



Considering this, there is something very remarkable in 

 the passage from Joule's paper of 1844 : — " Believing, as I 

 do, that the power of destroying things belongs to the 

 Creator alone, I entirely coincide with Roget and Faraday 

 in the opinion that any theory, which when carried out, 



