EXTENT OF EXPERIMENTAL WORK. 99 



is remarkable as containing the first definite dynamical 

 deductions ever made from gaseous hypothesis. It is also 

 the last mention Joule makes of this hypothesis, except the 

 mere mention, which he makes in 1848, in stating that he 

 adopts the hypothesis of Herapath, published in 1847, as 

 being simpler. 



Although Joule's earlier researches, those made before 

 August, 1843, which led him to the discovery of the 

 principal relations on which the law of conservation of 

 energy is based, and during which he acquired his unique 

 facility in quantitative measurement, must ever remain un- 

 rivalled in interest and importance by any of his subsequent 

 work, it is interesting to notice that his capacity for experi- 

 mental work has so far been steadily increasing. 



In the interval from the summer of 1843 to that of 1845, 

 besides the researches already mentioned, he* was engaged 

 on two other very considerable researches having a direct 

 bearing on the main line of his work. 



After Joule's discovery of the mechanical equivalent of 

 heat in 1843 the electro-magnetic investigation which he 

 was continuing with Dr. Scoresby was invested with a new 

 interest, and was continued with a view to comprising 

 the economic capabilities of electro-magnetism, steam, and 

 horses, as sources of power, and the comparison of the "work" 

 done with the heat equivalents of the zinc, coal, and food, 

 severally consumed by these sources of power. In 1845, 

 during the research, Joule spends some time visiting Dr. 

 Scoresby, at Bradford. The results of this research were 

 published in the PhilosopJiical Magazine in 1846, under the 

 title :— 



" Experiments and Observations on the Mechanical 

 Poivers of Electro-magnetism, Steam, and Horses. By the 



