474 FRAGMENTS OF SCIENCE. 



XIX. 



THE COPLEY MEDALIST OF 1870. 



rPHIRTY years ago Electro-magnetism was looked to 

 JL as a motive power, which might possibly com- 

 pete with steam. In centres of industry, such as 

 Manchester, 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 Stur- 

 geon's ' Annals of Electricity' between 1839 and 1841, 

 described various attempts at the construction and per- 

 fection of electro-magnetic engines. The spirit in 

 which Mr. Joule pursued these enquiries is revealed in 

 the following extract : ' I am particularly anxious,' he 

 says, ' to communicate any new arrangement in order, 

 if possible, to forestall the monopolising designs of those 

 who seem to regard this most interesting subject merely 

 in the light of pecuniary speculation.' He was natur- 

 ally led to investigate the laws of electro-magnetic 

 attractions, and in 1840 he announced the important 

 principle that the attractive force exerted by two electro- 

 magnets, or by an electro-magnet and a mass of an- 

 nealed iron, is directly proportional to the square 

 of the strength of the magnetising current ; while 

 the attraction exerted between an electro-magnet 

 and the pole of a permanent steel magnet, varies 



