for SAL io] 
LI. A curious electro-magnetic Experiment by P. Bartow, Esq. 
Royal Military Academy. In a Leiter to the Editor*. 
To Dr. Tilloch. 
Dear Sir,— Atrnoucu I am not aware that the following 
electro-magnetic experiment will throw any additional light upon 
the very interesting results of Mr. Faraday of the Royal Institu- 
tion, yet it is so very peculiar in the nature of its effects, and so 
pleasing in the exhibition, that it may be interesting to some of 
your readers who have the means of repeating it. ‘The machine 
is represented in Fig. 4 (Plate IV). AB is a rectangular piece 
of hard wood; CDE a piece of stout brass or copper wire ; 
and al cd, a rectangle of smaller copper wire (soldered at E) ; 
on the lower side of which the wheel W of thin copper turns 
freely: fg is a small reservoir of mercury sunk in the wood ; 
and gz a narrow channel running into it. HM is a strong 
horse-shoe magnet. 
Mercury being now poured into the reservoir fg, till the teeth 
of the wheel are slightly immersed in it, and the surface covered 
with weak dilute nitric acid, make the connexion with the bat- 
tery at 7 and D; and the wheel W will immediately begin to 
rotate with an astonishing velocity, far beyond the power of the 
eye to follow, and will thus produce the most pleasing effect. 
The galvanic apparatus which I employed to produce this 
motion was the calorimotor of Dr. Hare which I had made of 
the plates of my old battery, 20 of zinc, and 20 of copper, each 
10 inches square. But a much less powerful combination will 
be sufficient. 
The suspension of the wheel is shown in fig. 5, and it may 
be proper to add, that in order to ensure a complete contact, the 
two sockets and the ends of the spindle should be amalgamated, 
as also the tops of the points of the wheel. 
If the contact be changed, or if the magnet be reversed, the 
motion of the wheel will be reversed also ; but J find the best 
effect produced when the wheel turns inwards. 
Another curious experiment, and that on which the above is 
founded, is as follows: 
After having been repeating Mr. Faraday’s rotating experi- 
ment, the young man who was assisting me wished to try the 
effect of the horse-shoe magnet upon the freely suspended gal- 
vanic wire, as it hung with its lower end in the mereury. ‘The 
wire was immediately thrown into a rapid oscillating motion, 
* The Editor is happy to inform his readers that Mr. Barlow is printing 
a second edition of his Essay on Magnetic Attractions, which will also 
embrace the interesting subject of Electro-Magnetism. 
Vol. 59, No. 288, April 1822. Hh flying 
