Mr Barlow*^ Electro-Magnetic Experiments. 
mity of the battery, whereby the cylinder abed is made to be- 
come a part of the conducting wire, and it will be found to re- 
volve on its axis with a great velocity, fully equal to that of the 
magnet in the last experiment ; the direction of the motion, 
with the arrangement shewn in the figure, being from left to 
right, to a person coinciding in position with the magnet.” 
Exp. IV. “ To exhibit the rotation of the galvanic wire inde- 
pendently of the galvanic battery. 
“ For this purpose, we must employ the apparatus exhibited 
in Fig. 5., where ABCD is a small copper vessel about inches 
high, and the same in diameter ; abed is another small cylin- 
der of copper, of the same height, soldered to the former vessel 
at its lower end dc, a hole being left in the bottom of the former 
to receive it. The cylinder abed is therefore open, and will admit 
a cylindrical magnet to be passed up, and it will at the same time 
hold a quantity of dilute acid within the space AD dabc : BC Zz 
is a zinc cylinder, very light, of rather less altitude than the cop- 
per one. To the cylinders a b and Z z are soldered two copper- 
wires, as shewn in the figure, the upper one having a steel point 
proceeding from E downwards, and resting in a small metal 
hole at F, and consequently the cylinder Z z will be free to move 
upon its point of suspension at F. 
“ Things being thus prepared, and the acid placed in the 
cell as above described, insert through the interior cylinder the 
north end of a strong cylindrical magnet, and balance the whole 
apparatus upon it ; when immediately the zinc cylinder will be- 
gin to revolve, with a greater or less velocity, according to the 
strength of the acid, the freedom of motion, and the power of 
the magnet. I have frequently, with this simple apparatus, pro- 
duced a motion amounting to ISO rotations per minute. The 
only difference between this and the other rotations we have de- 
scribed is, that the galvanic power is here produced by the ap- 
paratus itself, instead of having recourse to the battery. 
“ For it is obvious, that the wire from Z z to E, may be 
considered as a conductor proceeding from the zinc, and the 
wire from ab to F, as one from the copper side of the bat- 
tery; and, consequently, the same effect is to be expected here 
as in the preceding cases. It is unnecessary to add, that, with 
