306 



M. Wilfrid de Fonvielle. 



[Apr. 15, 



piece, these experiments are rather tedious, as it is necessary to wait 

 for some minutes before knowing with certainty whether the rotation 

 is due to electro- magnetic reactions or to the mechanical impulse. 



All the effects exhibited with magnets and moveable pieces of iron 

 have the advantage of being produced without the help of any external 

 force other than magnetical attraction working at a distance. This it 

 is, I venture to think, what renders them so really effective. 



When the moveable pieces are star-shaped, or composed of a 

 number of iron pieces insulated magnetically, they are not moved 

 by themselves, except when they occupy certain positions in relation 

 to the position of equilibrium of a magnetic needle under the action 

 of a continuous voltaic current flowing through the coil. 



Under the same circumstances, the more arms the star possesses the 

 more easily it revolves. An even number of arms appears to be less 

 favourable to rotation than an uneven number. 



But the difference of the phenomena exhibited when there is no 

 magnet in operation is very striking, as there is then a definite direc- 

 tion of rotation, and if the moveable piece should be propelled in the 

 wrong direction, its velocity quickly diminishes, and the piece soon 

 rotates in the right direction, If the magnet is placed in a direction 

 perpendicular to the frame the rotation is stopped. 



A very small moveable piece has also been constructed so that it can 

 be placed in different positions in the interior of the frame. The position 

 of the axis within the frame involves no difference in the direction of 

 the rotation, although the velocity can be in some degree altered, but 

 it is not very easy to ascertain the fact, the velocity being so great 

 that very often the motion seems to be imperceptible to the eye. These 

 phenomena, which can be varied to any extent, as will be shown 

 hereafter, appear to be capable of a very simple explanation, by an 

 application of the laws of induction discovered by Faraday. 



The possibility of producing the same movement by means of 

 moveables of any form whatever, and notably of two spirals constructed 

 of a flat wire and wound in an opposite direction, appears to demon- 

 strate that the rotatory action is exercised individually on each molecule 

 of iron, and that the total impulse must be regarded as the integral of 

 the individual impulsive actions. This remarkable property appears 

 to furnish a very simple means of completely explaining all the 

 circumstances of these curious phenomena by means of the known 

 laws of induction, and to dispense with having recourse to any new 

 hypothesis. It is sufficient, in fact, to remark that the molecule of 

 iron acts in its movement of rotation in two different ways in each of 

 the two nearly equal currents of induction which successively traverse 

 the spirals, but the alternate appearances of which are separated 

 by very feeble intervals of time. In fact, during the whole continuance 

 of the two phases of rotatory movement which the galvanometric frame 



