178 Description of an Electro-motive Engine, 



Jacobi's engines. The workmanship may indeed be so per- 

 fect as to bring them very close without actual contact. But 

 the expansion and contraction of iron by change of tempera- 

 ture, renders it exceedingly difficult to adjust them so close 

 as delicacy of workmanship might otherwise admit of. These 

 disadvantages appear also to be augmented by enlarging and 

 multiplying the parts composing the engine ; and in propor- 

 tion, the loss of power and waste of materials will be greater. 

 However this may be, nothing short of actual contact can 

 render the whole power available, which is evidently imprac- 

 ticable in the rotating engines. 



These considerations naturally suggest the plan of causing 

 the keeper to be attracted and repelled alternately, this obvi- 

 ous movement being made to act as a motive power. In this 

 case, however, the limited distance at which the electro-mag- 

 net acts is by no means the only difficulty, — the adhesion of the 

 keeper,* even when contact is broken, is another, which is 

 not obviated by changing the poles. It occurred to me, 

 however, that by means of the mechanical contrivance here- 

 after described, and availing myself at the same time of the 

 residuum power remaining for a moment in all electro-mag- 

 nets, that the keeper could always be separated from the 

 magnet the instant it came in contact with it ; that by using 

 the contrivance, alluded to, the keeper never could adhere to 

 the magnet, and thus the strokes could be repeated rapidly 

 with the full power of the engine. This plan answers 

 perfectly. 



1 informed Mr. Palmer of Newgate street, of the result of 

 the above arrangement, in a letter dated 20th November 1843, 

 and his reply is dated the 28th December following. 



In my model there is no changing of poles, and the keeper 

 can be made to strike the face of the magnet from 150 to 200 

 times in a minute, with its full force, when not loaded. The 



* The clumsy and unscientific expedient of interposing slips of wood, or card, 

 to prevent contact and sticking, is hardly deserving of notice. 



