78 Intelligence and Miscellaneous Articles, 



ON A DIRECT TRANSFORMATION OF MECHANICAL WORK INTO 

 ELECTRICITY. BY E. GUIGNET. 



In most physical institutions we find electrical motors (Froment's 

 system more or less modified). The Ecole Polytechnique o£ Rio 

 de Janeiro possesses such a motor formed of five fixed electromag- 

 nets and a movable barrel furnished with six bars of soft ii'on. 

 The current of ten Bun sen elements being thrown into the wire of 

 tlie electromagnets, the barrel turns briskly from right to left, or 

 from left to right, according to the general direction of the current. 

 Moreover a commutator, carried by the axis, changes the direc- 

 tion of the current, in each of the electromagnets, at every fifth 

 part of a revolution. 



This apparatus has for a long time served for showing how an 

 electric current, whatever its origin, can produce work, doubtless 

 very costly, but of which the expense depends directly upon the 

 net cost of the current. The same apparatus can be used for the 

 inverse demonstration — a fact which appears to me important for 

 the instructor ; for the experiment is easily carried out in any lec- 

 ture-room. 



If the two extremities of the wire of the electromagnets be put 

 in communication with any galvanometer (which need not be very 

 sensitive), turning with the hand the barrel of the motor will be 

 sufficient to establish the formation of a continuous current whose 

 direction changes with that of the rotation. It can even be proved 

 thus that the intensity of the current increases with the velocity 

 of rotation, at least up to a certain limit. 



Finally, the same experiment makes evident induction under the 

 influence of the earth. Several contrivances have been devised 

 to render this curious phenomenon sensible — notably the inge- 

 nious hoop of M. Delezenne. In the foregoing experiment the 

 soft-iron bars become magnetized under the influence of the earth. 

 Their changes of position with respect to the fixed electromagnets 

 give rise in the wires to induction- currents which are gathered into 

 a single current by the commutators. Therefore the maximum 

 effect will be obtained when the axis of the barrel is parallel to the 

 inclination-needle ; but, on account of the charge on the cushions, 

 it is better to place the apparatus so that the axis is horizontal and 

 parallel to the declination-needle. 



It is likewise easy to show that the magnetization of the soft-iron 

 bars and of the electromagnets increases with the velocity of the 

 rotation. When the barrel turns very slowly, the two soft irons 

 scarcely attract iron filings, in consequence of the earth's magnetism; 

 but as the operation proceeds, when the velocity reaches several rota- 

 tions per second, the soft irons can lift large quantities of iron 

 filings. 



On replacing the bars of soft iron of the Froment motor by elec- 

 tromagnets wound round with a wire communicating with that of 

 the fixed electromagnets, a genuine dynamoelectrical machine would 

 be obtained, of the class of the Gramme machines without perma- 

 nent magnets ; but the performance of such a machine would 



