JOULE'S HISTORIC SKETCH. 133 



experiments of Rumford gave an approximate equivalent 

 of 1034 foot lbs. per i° of heat. He then describes Sir 

 Humphrey Davy's experiments of rubbing two pieces of ice 

 together until they were melted. He also mentions Dulong's 

 statement that equal "volumes of the same elastic fluids, 

 taken at the same temperature and under the same pressure, 

 being compressed or dilated suddenly, disengage or absorb 

 the same absolute qua7itity of heat" He then mentions the 

 works of Faraday, Grove, and Mayer, as preceding his own 

 early work in advancing the idea that the so-called imponder- 

 able bodies are merely the exponents of different forms of 

 force. He mentions the experiments of H. Seguin on steam, 

 as affording an approximate determination of the mechanical 

 equivalent, and finally says : — 



" The first mention, so far as I am aware, of experiments 

 in which the evolution of heat from fluid friction is asserted, 

 was in 1842, by M. Mayer, who states that he has raised 

 the temperature of water from 12 C. to 13 C, by agitat- 

 ing it, without, however, indicating the quantity of force 

 employed, or the precautions taken, to secure the correct 

 result." 



In this historic sketch, the measure of credit Joule gives 

 to the importance of the discoveries of his predecessors 

 is in no sense minimised or given grudgingly, but, on the 

 other hand, is ample (containing references to their work), and 

 only to be justified after viewing their results by the better 

 light of his own. He clearly does not view them as com- 

 petitors for fame, but as fellow-labourers in the task of 

 convincing the scientific world of its error, who afford 

 powerful advocacy to views he himself is advocating. 



It must, also, be doubted whether, but for this sketch, 

 the work of his immediate predecessors, Seguin and Mayer, 



