XIX. 



THE COPLEY MEDALIST OF 1870. 



PTHHIRTY years ago Electro-magnetism was looked 

 -L to as a motive power, which might possibly com- 

 pete 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 litera- 

 ture 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, de-* 

 scribed 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 

 naturally led to investigate the laws of electro-magnetic 

 attractions, and in 1840 he announced the important 

 principle that the attractive force exerted by two elec- 

 tro-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 at- 

 traction exerted between an electro-magnet and the 

 pole of a permanent steel magnet, varies simply as the 

 422 



