EFFECTS THE MEASUREMENT OF WORK. 35 



horse shoe magnets of definite proportions, with their poles 

 in the same plane in close order, which he finds " gives 

 good lifting power," the reasons for which he states. To 

 describe his success so far, and explain how he proposes 

 to adapt this to the machine, constitutes his first paper, 

 8th January, 1838. The problem before him is, how- 

 ever, not how to get the greatest lifting force out of his 

 magnets, but how to get the greatest amount of mechanical 

 work with the least weight of material out of a given 

 battery. He has not, apparently, paid any attention to 

 the problem of the battery. His second paper, December 

 1st, 1838, shows that when he sets his engine to work he 

 is face to face with the other factor of work — motion. His 

 engine has force but not speed. " I finished the engine I 

 was working upon last summer." It had thus occupied him 

 six months, a period which will not seem long, considering 

 that he did all the work himself, and did it with the utmost 

 care. In the next sentence he says : " It weighs 7^ lbs., 

 and the greatest power I have been able to develop with a 

 battery of forty-eight Wollaston four-inch plates was to raise 

 1 5 lbs. a foot high in a minute, in which the friction of the 

 working parts, which was very considerable, was reckoned." 

 In this sentence he uses 'power' in its accepted sense, 

 rate of motion against resistance ; and though he does not 

 introduce the expression 'work,' he has effected its measure- 

 ment and used it as expressing the mechanical potency 

 derived from his machine. The passage is thus remarkable, 

 as showing Joule's early appreciation of this fundamental 

 measure of mechanical action. It is also remarkable, as 

 containing the first recorded absolute measurement of 

 work in connection with the philosophical study of physics. 

 In his next sentence Joule remarks : " The result shows 



