34 STARTS TO IMPROVE STURGEON'S ENGINE. 



the apparent possibility " that electro-magnetism will ulti- 

 mately be substituted for steam in propelling machinery." 

 That he had any underlying philosophical motive in no 

 way appears. That he already possessed considerable 

 familiarity with the voltaic and electrical appliances then 

 in vogue is clear, but this is about all. He does not seem 

 to have, at this time, studied the philosophy of the subject, or to 

 have had any special acquaintance with the work of Oersted, 

 Ohm, or Faraday. Of mechanical philosophy he appears 

 to have had no knowledge beyond that which was familiar 

 to the practical engineers amongst whom he lived, and 

 what had resulted from his own observation. That he 

 possessed the engineer's rather than the philosopher's 

 knowledge of mechanics proved one of the happiest circum- 

 stances ; as he was thus familiar with the only measure of 

 mechanical action which directly measured the mechanical 

 effect of the physical actions he was about to study. 



As the purpose of the electro-magnetic engine, like that 

 of all prime movers, is to cause motion against resistance, 

 Joule was at once introduced to the measurement of the 

 physical actions in his engine in terms of 'work,' the only 

 measure of mechanical effect, but he did not at first 

 apprehend this in its full significance. The first thing 

 to catch his attention was how to increase the force 

 which the engine would exert. The " dynamo " is now, 

 as the "electro-magnetic engine" was then, essentially feeble 

 as regards effort. This effort depends on the attractive 

 force of the magnets, and Joule's first paper shows that his 

 attention was solely directed to the statical effect — how 

 with a given battery to obtain the greatest amount of force 

 out of the least weight of soft iron and wire ? He had con- 

 structed a compound magnet, consisting of small soft iron 



