XIX 



THE COPLEY MEDALIST OF 1870 



THIETY years ago Electro -magnetism was looked to 

 as a motive power wMcli miglit possibly compete 

 witli steam. In centres of industry, sucL. as Man- 

 chester, attempts to investigate and apply tliis 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: "I am 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) 



