TO THE MOVEMENT OF MACHINES. 509 
: Qn? fr m A y 
tion, we should have dq? oF double the previous action. We might 
even construct wheel-work in such a manner that the velocities of the sy- 
stems should be in the ratio of m:1, and that the poles should meet 
(m +1) times, during one revolution. The action would then be 
(m +1) n? oS and this increase would be gained by purely geo- 
metrical means. This is a simple deduction from the fact that velocity 
does not enter into magnetic attraction. I have not as yet availed 
myself of this advantage in the construction of magnetic apparatus, 
since there are some remarkable circumstances, as we shall see here- 
after, not sufficiently cleared up, and which may give rise to consider- 
able modifications. 
6. 
The inversion of the poles is an object of the greatest importance. 
This inversion should take place instantaneously, and precisely at the 
place where the poles are situated opposite to one another. The me- 
chanism intended to produce this operation should be put in motion by 
the apparatus itself, but no element should be introduced which is 
dependent in a geometrical manner upon the rotatory movement of the 
system. The velocity of the motion, however great it may be, should 
not at all affect this operation. The well-known bascule, an ingenious 
invention of M. Ampére, which is so advantageously employed in electro- 
magnetic experiments, cannot be employed in the magnetic apparatus 
with a continuous circular motion; for the number of inversions, in a 
given time, cannot be considerable without requiring extraordinary means; 
and even these means willnot guarantee the certain result of anadvancing 
and receding movement, repeated as frequently as may be necessary. 
I shall not recount here all the attempts I have made, both numerous 
and expensive, to arrive at the important result of an inversion of the 
poles, exact and precise, divested at once of every element depending 
on the velocity. Butit is necessary to say that the greatest difficul- 
ties arose by employing mercury, as is usual in electro-magnetic 
experiments to form and to break metallic contact. In the liquid 
state the adhesion of the mercury to the metallic body plunged into 
it and afterwards withdrawn, varies with the rapidity of the motion and 
with the purity of the mercury. Frequently—I may say always— 
the inversion takes place too soon or too late, and thus gives rise to an 
attraction or repulsion, in a contrary direction to the rotation. More- 
over it is very difficult to preserve the mercury pure when in contact 
with other metals; and even the purest mercury is disposed to oxidize 
easily under the influence of the electric sparks. These sparks are pro- 
duced, under favourable circumstances, on establishing metallic con- 
tact, and always on breaking it. The result is, that the surface of the 
