1880.] 



On an Electro-Magnetic Gyroscope. 



307 



brings closer together, each molecule of soft iron increases the intensity 

 of the current which affects it, and which, independently of its real 

 direction, the author calls 'positive, in order to fix the ideas ; at the 

 same time it diminishes that of the current which repels it, and which, 

 for the same reason, is called negative. In two other phases of its 

 movement the same molecule diminishes the intensity of the positive 

 current, which then tends to draw it back, and increases that of the 

 negative current, which turns it away from the frame. The actions 

 exerted in the two phases of the movement, that is, in the total extent 

 of the plane described by the molecules, tend then to keep up the con- 

 tinuous rotation, which progressively increases in speed until it reaches 

 that which corresponds to the absolute intensity of the attractions or 

 repulsions exercised by the currents induced by the energy of the 

 inductive current, the value of the friction of the resistance of the arc, 

 and other occasions. 



When we bring the pole of a magnet into action, it is clear that its 

 influence determines in each of the molecules of the moveable object a 

 transient magnetisation which strengthens the induction currents pro- 

 duced in the spires in the cases in which it is concordant, and which 

 paralyses them in the opposite case. It hence results that, in presence 

 of a permanent magnetic centre, the movement is possible only in a 

 direction determined by its position and its nature. The author 

 believes that this principle applies even to the action of the earth. 



When we change the position of the active pole in relation to the 

 axis of rotation, the rotation changes its direction; but the pole of 

 the magnet may be placed above or below, to right or left, without 

 the rotation changing its direction. The two poles of a bar or a horse- 

 shoe-magnet combine to accelerate the movement when they are 

 placed in the direction of the frame ; but if we place the magnet in a 

 perpendicular direction, all movement is, as a rule, rendered impossible. 

 It is the same with near position ; in proportion as we approach it 

 to that limit of position, the rotation in general will be found to 

 slacken. It is clear that a magnetisable body so strongly tempered as 

 not to have the capacity of being magnetised and demagnetised to the 

 given extent, will remain insensible to these successive dynamic re- 

 actions, and consequently immoveable, and that it is necessary to 

 employ the softest possible iron in the construction of the moveable 

 objects. The same phenomena, especially with the spiral, may evi- 

 dently be produced if we place it about the frame. They are accom- 

 panied, especially with the full disk, by a strident sound, arising from 

 the alternate magnetisations and demagnetisations ; and this fact seems 

 to be a new confirmation of the theories which have been advanced. 



I must not omit to mention also a number of other phenomena 

 which at least, in some respects, can be quoted in support of that 

 opinion which my friend, M. Lontin, considers also as being valid. 



