TO THE MOVEMENT OF MACHINES. 527 



helix in which a magnet is inserted. This is the explanation of the 

 problem of the unifonn rapidity of the magnetic machine ; for, being put 

 in motion by the magnetizing power of a voltaic current, it represents 

 simultaneously an apparatus composed of magnets in motion, and ca- 

 pable of producing a magneto-electric current, in a direction contrary 

 to the voltaic current. The first is closed by the pile itself, which, being 

 comjjosed of a single pair only, does not offer too great a resistance to 

 its passage. 



In the connecting wire, formed by the union of the sixteen helices of 

 the apparatus, I interposed a galvanometer ; and then, by closing the 

 circuit and preventing the motion of the machine, I observed the devia- 

 tion of the needle : it amounted to nearly 60°. As soon as the motion 

 of the appai'atus commenced the needle began to recede, and continued 

 to do so more and more as the speed became more accelerated. The 

 motion having become uniform, at the rate of 60 revolutions in a mi- 

 nute, the needle became stationary at a deviation of about ^V". The 

 needle always advanced when the motion was stopped or retarded ; it 

 receded, on the contrary, when it was mechanically accelerated. It ap- 

 pears that the deviation of the needle of 47° corresponds with the state 

 of equilibrium; for the motion having of itself ceased, the needle did 

 not quit this position. Thus in the different experiments, whether the 

 first deviation of the needle exceeded 60°, or was less, it always became 

 fixed at about 47°. The voltaic current having been weakened by the 

 interposition of different branches, until the first deviation amounted 

 only to 47°, the magnetism was not sufficiently strong to produce the 

 movement of the apparatus. Repeated experiments will be necessary 

 to investigate these interesting phasnomena. 



19. 

 I imagined that it would be useful to open two passages or two 

 separate branches to the magneto-electric current ; one of which should 

 be the pile, and the other a second connecting metallic wire, so long and 

 so thin as not too much to affect the quantity of electricity passing 

 through the principal connecting wire. (Art. 8., No. 6.) There was 

 reason to suppose that the counter-current would rather follow the 

 metallic wire than the liquid of the pile : but it was not so. Du- 

 ring the motion of the apparatus, the needle of the galvanometer 

 being fixed at 47°, and the second circuit having been suddenly esta- 

 blished, the needle was not much affected by it. It advanced, it is 

 true, but only 1°*5. Neither did the speed of the apparatus sensibly 

 change. On reducing the length of the second wire it was nearly the 

 same. The passage of the counter-current across the metallic wire 

 was proved, at least in part, by the interposition of a second galvanome- 

 ter. During the accelerated movement the needle of this latter ad- 



