TO THE MOTION OF MACHINES. 531 
advanced and receded by the arrangements above mentioned respec- 
tively to 30° and 40°. We see that in this case the needle is rather 
less affected than in the case of the disjunction of the second wire; but 
I expected, as a necessary consequence, that the needle would not be 
at all affected, for I had received no shock nor spark in the analo- 
gous experiment. I confess that at present I am unable to enter into 
an explanation of the striking difference which subsists between the 
current of reaction and the magneto-electric current. 
ae 
With regard to the magnetic machine, it will be of great importance 
to weaken the effect of the counter-current, without at the same time 
weakening the magnetism of the bars. It is the alternate combination 
of the pairs of plates or the voltaic pile which permits us to increase 
the speed of rotation at will. We know that the magnetic power of 
the current is not sensibly augmented by increasing the number of the 
pairs of plates, but the counter-current is considerably weakened by 
it, being forced to pass through a great many layers of liquid. In 
fact, on using twelve voltaic pairs, each half a square foot, instead 
of four copper troughs, each with a surface of two square feet, 
which I had hitherto used, the speed of rotation rose to at least 250 
—300 revolutions in a minute, a number which I was able only to 
estimate, having been unable to count them. The acid which I em- 
ployed was extremely weak, and had served for many previous experi- 
ments. The development of gas was imperceptible either by sight or 
smell. Having immersed two thick copper wires in the cups p and 9, 
and having taken hold of them with my hands dipped in salt water, I 
received during the motion of the apparatus violent shocks, and felt 
an extreme pricking sensation in the upper part of my body. The 
mechanical effect of the apparatus corresponding to the speed of 250 
to 300 revolutions in a minute has been valued at half the force of a 
man. I shall at a future time apply to it an exact dynamometric 
apparatus. 
I have not been able to make further experiments on this subject, 
and I am obliged to interrupt my investigations for a time; but from 
what precedes, I may perhaps be justified in maintaining, that the su- 
periority of this new motor, with regard to the absence of danger, the 
simplicity of the application, and the expense of the materials necessary 
to keep it in action, is placed beyond doubt. 
Vou. —Parrt IV. 20 
