DOUBLE-CURRENT MAGNETO-FARADIC APPARATUS. 271 



C. — The regulator of the armature. 



The movable plate G, upon which are placed the armature and 

 its motor system, is approximated to or removed from the magnet, 

 by means of a strong screw N, called the regulator of the arma- 

 ture. This screw, turning in a nut fixed to the apparatus, acts 

 upon the base of one of the mounts which forms part of the plate 

 G, which it moves backwards and forwards. 



In order that the armature may exercise a tension uiDon the 

 magnet, the screw N is turned in sucli a manner that the needle is 

 brought to the middle part of the arc of a circle 0, which is called 

 the indicator. Then the armature, placed transversely, is brought 

 near to the magnet, and is in contact with its extremities. 



We shall see hereafter in what ^\ay the reguhitor of the arma- 

 ture serves also to weaken or to moderate the ii'duction currents. 



J).~The coils. 



A reel nine centimetres and a half in length, and upon which 

 twenty-fouv metres of copper wire, covered with silk, an 1 half a 

 millimetre in diameter, are rolled spirally, is fixed to each arm of 

 the magnet, in such a manner that its anterior bonier is level 

 with the free edge of the magnet. The rounded anterior extremity 

 of the reel rests in a support wliich maintains the magnet in 

 a position parallel to the plane of the apparatus. 



A second copper wire, the sixth of a millimetre in diameter, six 

 hundred metres in length, and covered with silk, is rolled over the 

 thicker wire, and forms a second coil. The thick wire is inductive 

 relatively to the thinner wire, which is induced by it. I shall 

 demonstrate this hereafter. 



The two superposed copper wires are rolled in the same direction, 

 and the extremity of the one is soldered to the commencement of 

 the other, while the other ends are brought, that of the thick wire 

 (central) to the springs S and S', which produce the intermissions 

 on the reel B, and that of the fine wire (external) to the 

 right side, IJ, of the commutator of the coils T, which conveys 

 the current of the primary coil to the knobs P and P', to which 

 are attached the conductors of the rheophores. The spring S' gives 

 origin to a conducting wire which proceeds to the left side of the 

 commutator T. 



E. — The Rheotome. 



The rheotome is composed of a small wooden reel, B, and of two 

 springs, S and S'. The reel is fixed upon an axis of soft iron. 

 One of the springs, S, in relation with one extremity of the central 



