Star.
London, England, 1824-05-08 00:00:00

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NS, in the figure, is the magnet ; P c P a piece of
platinum wire bent into the form a semicircle or
other convenient curve; Ps, Ps are two pieces of silver
wire twitted to the former at the extremities P P. The
other ends of the silver wire; are bent downwards at
s;s and made quit:: sharp and smooth at the points.
These points descend into the metallic cell F E, which
contains pure quicksilver, with which the points com-
municate. A descending pcint c soldered to the pla-
tinum wire, forms the pivot on which the moveable
part of the machine turns. A small concavity well
polished at the bottom is mace in the point of the
magnet for the purpose of containing a small globule
of mercury,and likewise for the rotating pi v ct to work in.
The point c being amalgamated, when it is placed in
thi, globule of mercury, forms a communication with
the magnet ; and the other part of the magnet which
passes through the cell communicates with the mercury
in that cell : and the points a the silver wires being
immersed in this mercury, the metallic circuit is thus
rendered complete; first, through the platinum wire
from P to c ; thence through the pivot to the top of the
magnet, and along that part of the magnet from the
top to the quicksilver in the cell F E: and lastly, along
the silver wire from the points to the extremity at P,
where it joins the platinum.
The other part of the wire machine being on the
same principle as that described, the platinum arms of
this apparatus, when heated by a spirit lamp or other-
wise at the extremities PP, are in every respect assimi-
lated to the arms of the rotating cylinder of Ampere ;
for the electric fluid is transmitted in the same dime-
tion through both au ms of the apparatus ; and hence
the rottiting tendency is coastant round a central mag-

net ; and not irnpr.Live, as in other rotations with an ex-
ternal magnet.
The moveable part of this machine (which is the pla-
tinum and silver wires only) will rotate with a facility
proportioned to the delicacy of the suspension, the dif.
ference of temperature of the parts P and c of each
arm, the power of the magnet, and the dexterity of the
experimenter. And I must here warn the Reader, that
this last requisite is not the least to ensure success in the
experiment ; for had I not been satisfied that the appa-
ratus was constructed upon principle, I probably might
not have persevered sufficiently to attain my object.,
llowever, a slight modification of the apparatus consi-
der ably facilitates the experiment, and renders it more
permanent and beautiful.
A circle of lamps are placed on a stage of the same
figure, in such a manner that they may coincide with
the periphery of the circle described by th? poilts P P
of the wire part of the machine, so that the latter may
constantly be kept at nearly the same temper :tore in
every part of their revolution. And the shoulder of
those arms, or that part of the platinum wire to which
the pivot c is soldered, is kept at as Dow a temperature
as possible, by means of ether or other cooling liquid.
If, instead of lamps, a circular flame of ignited hy-
drogen be substituted, and regulated by a stop-cock,
this part of the apparatus may perhaps be considered
at its acme of perfection.
Another improvement is by having a conducting
wire from the pivot c to the metallic cell FE, in the
same manner as the conducting wire of the copper part
of M. Ampere's rotating cylinders ; through the upper
part of this conducting wire passes a screw with a
milled head, made into the form of a cop. The pivot
c runs in this cup, at the bottom of which is a small
globule of mercury, for the better ensuring the contact.
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The cup is then filled up with ether, and may be supplied
during the experiment in proportion to the evaporation.
The lower end of this screw rests in the bole in t:lc
top of the magnet; and by turning the milled head to
the right or left, the points ss of the silver wires may
he heightened or lowered at pleasure; and con,equently
their contact with the mercury in the "cell F E may be
reptlated to the greatest nicety ; the attainment of
which was the only embarrassment I had to encounter
with the original apparatus. However, by means of this
improvement, my anticipations were soon agreeably
realized by witnessing th.l first thermo-rotation ever
produced by the influence ofd central magnet.
I must here beg leave to observe, that the only at-
tempt I ever heard of (and the only one perhaps on re-
cord) was with the apparatus of Professor Cumming,
and a similar attempt by Professor Barlow with a com-
bination upon the same principles.
The latter Gentleman, however, has candidly con-
fessed the failure of the experiment, and sufficiently ac-
counted for the inefficacy of the apparatus upon the
principle of its construction.

I am, Gentlemen, your's respectfully,
Artillery-place, Woolwich. WNI. STURGEON.

P.S.—April 13. I have since succeeded in forming
a sphere of galvanited wiles, to rotate by the influence
of both poles of an internal magnet.
This experiment was suggested on reading the late
Dr. Halley on the theory of the earth ; and although
it may not be considered as a proof of that philoso-
pher's notion of terrestrial magnetic variation, yet per-
haps it may tend in some measure to strengthen the hy-
pothesis. A description of the apparatus shall be the
subject of another paper. W. S.

M. BELZONI.