358 Electro-Magnetic and Magneto-Electric Pormula. 



to measure the quantity of electricity and not its tension, indi- 

 cates, on the contrary, a decrease of strength. 



Several variations of this experiment are easily deduced from 

 the figure given above, (fig. 3,) which may be considered a gen- 

 eral magneto-electric and electro-magnetic formula. In order to 

 justify the idea of using the figure of man, we will request our read- 

 ers to peruse what Mr. Pouillet says on the subject of the elec- 

 tro-magnetic figure of Mr. Ampere.* The two stars on the head 

 of those two figures are the symbol of the two electricities at the 

 moment they unite, and the position of the same figures indi- 

 cates the movement of the electric spark, as going from above 

 downwards, and it is in fact thus that lightning (foudre) or- 

 dinarily moves. They know that this movement, from above 

 downwards, of the electric spark produces magnetization all 

 around it and in a plane perpendicular to its direction, and the 

 whole passes exactly in the same manner as if the magnet- 

 ism wei^e conveyed by an austral pole, (that is to say, the pole 

 of a magnetized needle directed to the north,) which is con- 

 ducted in the same plane on the left, (from the west south- 

 ward, towards the east, &c.,) and by a northern pole inseparable 

 from it, which is conducted to the right, (from the east south- 

 ward, to the west, &c.) It is thus that the figure A turning to 

 the left, is the symbol of the austral magnetism, and the figure B 

 turning to the right, that of the northern magnetism. 



It is seen then that the direction of the spark or of the electric 

 current, is indicated by the situation of these two figures, and that 

 the movement of these same figures expresses the situation of the 

 magnetic pole according to all the tangents, which, as indicated 

 by this motion, are all comprehended in a plane perpendicular 

 to the direction of the spark. All that is essential to electro- 

 mgnetism being thus explained, our design is evidently a gen- 

 eral symbol of the electro-magnetic phenomena, or a general 

 formula, the application of which to all particular cases is very 

 easy. 



But this design is also a general magneto-electric formula. 

 If, for example, the south pole of a magnet enter into an 

 helix of copper wire, it produces evidently a separation of the 

 magnetic fluid, since the northern magnetism is attracted and 



* Pouillet, Elem. de Phys. exp. Paris. 1832. Tom. I. P. 2. p. 242. 



