HISTORY, &c., OF INDUCTION INSTRUMENTS. 



289 



Fig. 69. — Theory of Pixii's arrangement. 



in order to work a commutator, which, on account of its com- 

 plexity, has not been represented in the figure. It is enough to 

 say that this part of the apparatus had for its office to conduct the 

 induced current always in the same direction. Clarke's instru- 

 ment will presently furnish us with an example of a contrivance 

 which is more simple, and better adapted to its purposes. 



"We can produce, by the aid of Pixii's instrument, all the 

 ordinary effects of induced currents, — heat, light, chemical decom- 

 positions, &c. 



" In order to explain the effect of the arrangement which has 

 been described, let A and B (fig. 69) be the projections of the 

 reels, and N and S the poles of 

 the magnet, on the plane described 

 by them in their movement of 

 rotation, which is supposed to 

 occur in the direction indicated 

 by the arrows. 



" The pole N retires from the 

 wheel A ; the pole S approaches 

 it ; as the two poles are of con- 

 trary names, their actions upon 

 the reel A concur. 



'• They concur also upon the reel B, but the current originating 

 in this reel is the opposite of that which originates in the reel A ; 

 and for these currents to combine it is only necessary to connect, 

 in a convenient manner, the wires which are rolled round the 

 reels ; and it is sufficient for this, that, if we suppose the horse- 

 shoe-shaped iron to be set upright, the wire should be wound in 

 the same direction round both its branches. 



"The inductive action is at its minimum when the poles are 

 equi-distant from the reels, but it does not cease. At the moment 

 when the poles are very near the reels, the action is much greater, 

 and it attains its maximum when the poles are opposite the reels ; 

 but at this moment the induction changes its direction, because 

 the movement which approximated each of the poles to tlie reel 

 before which it passed, then removes it." 



After having described the apparatus of Pixii, M. Le Eoux has 

 stated the following theory of magneto- electric instruments, which, 

 by reason of its novelty and importance, merits to be here repro- 

 duced : — 



" The curve of the intensities of the current may be exhibited 

 as in fig. 70, where the distance Aq and Bq represents the time in 

 which each pole passes from the reel A to the reel B, and so on. 



" In reality, the passage from the positive arc, a m h, to the 



u 



