JOULE'S MOTIVE. 



also secured a place in the history of the Royal Society. 

 This paper was published in the PJiilosophical Magazine 

 early in 1841, with a slightly extended title. 



Joule makes no explicit statement as to what starred 

 him on this research, but this may be easily inferred. He 

 had started his magnetic experiments, and continued them 

 for nearly three years, under the impression that the resist- 

 ance encountered by the electrical current in the wire on 

 his magnets was simply the ordinary resistance of the wire, 

 and was therefore the same, whether the engine was 

 stationary* or working. His philosophical attention had been 

 directed solely to the arrangement of the electro-magnets, 

 taking the phenomena of the battery and current for granted, 

 as things familiar to him, which so far did not excite his 

 philosophical curiosity*. When, however, he came to measure 

 the current, discovering that it was subject to an increased 

 resistance when the engine was working, and further, that the 

 electromotive force necessary to overcome this increased 

 resistance was proportional to the work done by the engine 

 (things he was not previously familiar with), his curiosity 

 became excited by the phenomena of the batten* and 

 current To satisfy this, he studied the researches of 

 Faraday 'then just published in a collected form), which 

 made him acquainted with the works of others, which he 

 also studied. This reading, which brought to his knowledge 

 many facts that he was not previously acquainted with, also 

 further excited his curiosity bv revealing to him the incom- 

 plete state of knowledge as to the quantitative relation 

 amongst the various physical phenomena, and particularly 

 with regard to the effect of a battery in producing heat in 

 the conductors. He had discovered for himself that the 

 mechanical effect produced by his engine was propor- 



