XIX 



THE COPLEY MEDALIST OF 1870 



THIRTY years ago Electro -magnetism was looked to 

 as a motive power which might possibly compete 

 with steam. In centres of industry, such as Man- 

 chester, attempts to investigate and apply this power were 

 numerous. This is shown by the scientific literature of the 

 time. Among others Mr. James Prescot Joule, a resident 

 of Manchester, took up the subject, and, in a series of 

 papers published in Sturgeon's "Annals of Electricity" 

 between 1839 and 1841, described various attempts at the 

 construction and perfection of electro-magnetic engines. 

 The spirit in which Mr. Joule pursued these inquiries is 

 revealed in the following extract: "lam particularly anx- 

 ious," he says, "to communicate any new arrangement in 

 order, if possible, to forestall the monopolizing designs 

 of those who seem to regard this most interesting subject 

 merely in the light of pecuniary speculation. ' ' He was 

 naturally led to investigate the laws of electro- magnetic 

 attractions, and in 1840 he announced the important prin- 

 ciple that the attractive force exerted by two electro-mag- 

 nets, or by an electro- magnet and a mass of annealed iron, 

 is directly proportional to the square of the strength of the 

 magnetizing current; while the attraction exerted between 

 an electro- magnet and the pole of a permanent steel mag- 

 net varies simply as the strength of the current. These 

 (444) 



