WATKIN’S MAGNETO-ELECTRIC INDUCTION. 
341 
Tiie drawing vfliich accompanies this cora- 
niunication represents my apparatus. In ar- 
rangement it varies very little from that of 
Mr. Saxton’s, the difference being merely in 
this respect, that Mr. Saxton places the axis 
wdiich carries his main revolving permanent 
magnet outside of the electro-magnet, while 
my axis is situated inside. The only advan- 
tage I obtained is that the apparatus is much 
more compact. Were this all I have to ad- 
vance on the subject, I sliould not trouble 
you with tlie present communication ; but as 
I have added seven permanent magnets in 
different situations, and succeeded in obtain- 
ing continued rotatory motion in all. I con- 
ceive that 1 have thus rendered the magnetic 
tov somewhat more interesting. 
The rev>)lving magnets I have had in mo- 
tion foreleven hours without superintendence, 
and they were only stopped when my worlc- 
shop was closed for the day. The chemical 
action on the copper and zinc elements of the 
voltaic battery employed to induce polarity 
in the soft iron by means of the copper wiie. 
surrounding it, is produced merely by salt and 
water (not nearly so strong as sea water); 
and I have a solution of this kind constantly 
in use. which has been nuxed above a month, 
and when the metallic elements are now 
placed in it. the magneto-electric machine in 
question acts without sensible diminution of 
force. 
The pendulum and suspended magnetic 
needles of this toy at times exhibit in a beau- 
tiful experiment of M. Plateau recordeil in 
Correspondence Mathematiqne et Physique, 
par M. Quetelel, tom. vi, p, 70 (1830). 
(a). A piece of soft iron bent in the form 
of a horseshoe magnet, paitly surrounded as 
at A by copper w’ire covered with silk in the 
usual manner. 
(c) . A permanent magnetic needle revolv- 
ing on an axis as represented in the figure, 
which axis has a contrivance of points dip- 
ping successively into a divided cup of mercu- 
ry, oue division of which is in connexion with 
the zinc element. The cup for the mercury 
cannot conveniently be shown in this figure, 
but it is placed so that the points on the axis, 
which have the efFect of changing the current 
in the copper wire enveloping each arm or 
branch of the soft iron, may dip into it suc- 
cessively as the axis rotates. 
(d) . A cup of mercury connected with one 
end of the copper wire coiled on the arms of 
the soft iron, while the other end of the wire 
is immersed in a similar cup situated at the 
other end of the axis, which it was impossible 
to show in the figure. 
. (eeeeee). Traversing magnetic needles; 
two, e S, revolve in a horizontal plane, the 
five former in a vertical plane. 
(/). A pendulum, consisting of a magnetic 
bar suspended by one end, which oscillates as 
already described. 
(g ^ g)’ A. mahogany stand or base for 
supporting the apparatus.’^ 
SAFETY OF LEAD PIPES PROTECTED 
BY TIN. 
(Extract of a letter from Mr. G. Chilton, 
dated Neio-York, June 23, 1834.^ 
Dear Sir, — Obseiving, in a late number, 
a notice of E w bank's tinned lea l pipes, 
and having- had many applications for infor- 
mation concerning tlie danger attending the 
use of metal pipes for conveying water, beer, 
cider, &c., I have been induced to subject the 
pipes of Ewbank to a lew trials, for the pur- 
pose of ascertaining whether, from the occa- 
sional contact of acids, any deleterious solu- 
tion of lead would attend their ordinary use. 
^ Abridged fijom the Philosophical Magazine, 
No. 38. 
