HISTORY, &c., OF INDUCTION INSTRUMENTS. 293 



of slight intensity. The power of the shock may be increased 

 by utilizing a final extra current that may be produced by the 

 following contrivance. 



" The metallic plates M and N, communicate with the conductors 

 R and S, which are represented in fig. 74, and the circuit being 

 completed by any part of the human body, if we then make a com- 

 munication by a metallic arc between the two half-cylinders, the 

 current will take, by preference, this direction, in which the resist- 

 ance is extremely weak, rather than pass through any part of the 

 body, so that the latter will receive scarcely anything ; and, more- 

 over, the current of the reels will have its maximum of intensity 

 for the given speed of rotation of the instrument, since the external 

 resistance is almost nil. If we then interrupt the metallic com- 

 munication between the two half-cylinders, the intensity of the 

 current will be reduced almost to zero by the great resistance of 

 the human body, and it will induce in the reel a current of inter- 

 ruption, of which the intensity is very great, as its electro-motor 

 force is considerable ; and which, during its short duration, will 

 possess a new physiological quality. 



" This extra current will be stronger, in proportion as the cur- 

 rent, by the interruption of which it was engendered, was itself 

 more powerful ; and it ought, therefore, to be produced at the 

 moment of coincidence of the poles with the reels." ^ 



E. — Pages instrument. — "When we approximate, or remove, 

 a piece of soft iron to or from the polar extremities of the per- 

 manent magnet, we produce in its branches variations of magnetism 

 which may be used for the induction of a circuit. This has been 

 done by the American physician, who has given his name to the 

 instrument next to be described. 



" Page has surrounded the extremities of the branches of a per- 

 manent magnet with coils of fine and long wire ; and by means 

 of a screw, worked by the handle D (fig. 75), this magnet can be 

 moved nearer to, or farther from, a bar of soft iron, E F, which is 

 mounted perpendicularly upon an axis, carrying a pinion to which 

 rapid movement can be communicated by a large toothed wheel. 

 The movement of the magnet is a means of graduating the inten- 

 sity of the currents that are produced. These currents are con- 

 nected, as in Clarke's machine, by a commutator mounted on the 

 same axis as the soft iron ; to this is added an interrupter, K, of the 

 same kind as has already been described, and which is arranged for 

 the production of an extra current, required for physiological action. 



" In the instrument shown in fig. 75, the position of the commu- 



* Le Rous, p. 30. 



