invented by M. Marie Davy. 491 



In most of the rotatory electro-magnetic machines hitherto 

 constructed, the moveable armatures pass rapidly before the 

 fixed electro-magnets, following a line perpendicular to the axis, 

 without coming into contact ; thus the entire amount of work 

 that might be obtained is not made use of. We must, however, 

 refer to the fact, that M. Froment, who has paid much attention 

 to electro-magnetic motor apparatus, has constructed a machine 

 in which an interior wheel, furnished with armatures of soft 

 iron, revolves upon the terminal faces of the fixed electro- 

 magnets, so as to make use of the magnetic attraction even up 

 to the point of contact of the magnetized surfaces; but this 

 arrangement produces, during the action of the machine, a 

 series of shocks or concussions, which are opposed to the con- 

 struction of a powerful machine upon this model. 



M. Marie makes the moveable electro-magnets or armatures 

 revolve in such a manner as to approach the fixed electro- 

 magnets in the direction of the axis up to the point of contact, 

 without any shock. Upon this principle are constructed the 

 two electromotive machines described in his note, one of which 

 has a continuous rotatory, the other an oscillatory motion. We 

 shall only refer to the former apparatus, of which he has pre- 

 pared a model, which has worked in our presence. 



This machine consists of sixty-three electro-magnets arranged 

 at equal distances round a circle of wood, furnished internally 

 with a circle of copper. All the electro-magnets have their axes 

 directed towards the centre of the wheel, and their surface 

 coincides with the concave surface of the copper circle. 



In the interior of this large wheel there are two others, of 

 which the radius is one-third of that of the former ; these are 

 also furnished with a circle of copper, and bear each twenty-one 

 equidistant electro- magnets, of which the axes are directed 

 towards the centre, and the polar surfaces coincide with the 

 concave surface of the copper wheels; these little wheels can 

 then revolve, without slipping, in the interior of the large wheel, 

 and carry round by their movement the axle of the machine, 

 which corresponds with the axis of the large wheel. The move- 

 able electro-magnets come successively in contact with the fixed 

 electro-magnets. The large and small wheels are furnished 

 with teeth for the maintenance of the coincidence, when this is 

 once established. 



The machine is also provided with various pieces of apparatus 

 for putting each of the electro-magnets successively in commu- 

 nication with the battery, and giving a different magnetization 

 to the two electro-magnets at the moment when they act upon 

 each other. 



M. Marii^ has made a change which appears advantageous. 



