358 Electro-Magnetic and. Magneto-E lectric Formula. 
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 infact 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 were 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, éc.,) and by a northern. pole inseparable 
from it, which is conducted to the right, (from thé 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 eireh tae of which to all particular cases is very 
But this design is— ale a sige magnefo-clectrie formula. 
If, for example, the south pole of a magnet enter into an 
helix of copper wire, it produces evidently a separation.of the 
riba fluid, since the northern a is attracted and 
. Ponillet, Elem. de Phys. exp. Paris. 1692 Tom. I. P. 2. p. 242. 
he ee ; ¢ f 5 = - 
