CHAPTER V. 



Third Research. — Heat Generated or Transferred. — 

 Arrangement not Generation of Heat in Voltaic Appa- 

 ratus. — The Heat Developed in the Entire Circuit by 

 Magneto-Electricity not the Result of Arrangement. — 

 Discovers Heat in the Revolving Armature. — Determines 

 Relation between Heat and Electric-Action ; the Same as 

 with Voltaic Ctcrrent. — Generation and Destruction of 

 Heat by Mechanical Means by the Agency of Magneto- 

 Electricity. — Constant Ratio betzveen the Heat and the 

 Power. — First Determination of the Mechanical Equiva- 

 lent of Heat. — The Climax of Joule's Researches. — 

 Attends British Association at Cork, 184.3. — Dazzled by 

 Possibility of Practical Residts. — Conclusions not Alto- 

 gether Justified. — Postscript. — Mechanical Effect Con- 

 verted into Heat by Friction. — Law of Conservation 

 Realized. 



In his paper, read before the Literary and Philosophical 

 Society, January 24th, 1843, in his fifth observation Joule 

 had said : — " The magnetic electrical machine enables us to 

 -convert mechanical power into heat by means of the currents 

 which are induced by it." Further consideration, however, 

 ^seems to have suggested to him that this point was still 

 lacking experimental proof ; for his next research is, in the 

 first place, obviously and avowedly directed to ascertain 

 whether the heat which is rendered apparent in one part of 



