Natural Philosophy.- — Electro-Magnetism. 179 
enougli to move the wire and the pole with considerable rapidity. 
It consists of a stand, about three inches by six, from one end of 
which a brass pillar rises about six inches high, and is then con- 
tinued horizontally by a copper-rod over the stand ; at the other 
end of the stand a copper-plate is fixed with a wire for commu- 
nication, brought out to one side ; in the middle is a similar plate 
and wire ; these are both fixed. A small shallow glass cup, 
supported on a hollow foot of glass, has a plate of metal cement- 
ed to the bottom, so as to close the aperture, and form a con- 
nexion with the plate on the stand ; the hollow foot is a socket, 
into which a small cylindrical bar-magnet can be placed, so that 
the upper pole shall be a little above the edge of the glass ; mer- 
cury is then poured in until the glass is nearly full ; a rod of 
metal descends from the horizontal arm perpendicularly over this 
cup ; a little cavity is hollowed at the end and amalgamated, 
and a piece of stiff copper-wire is also amalgamated, and placed 
in it being attached by a piece of thread in the manner of a li- 
gament, passing from the end of the wire to the inner surface 
of the cup ; the lower end of the wire is amalgamated, and fur- 
nished with a small roller, which dips so as to be under the sur- 
face of the mercury in the cup beneath it. The other plate on 
the stand has also its cup, which is nearly cylindrical, a metal- 
pin passes through the bottom of it, to connect by contact with 
the plate below, and to the inner end of the pin a small round 
bar-magnet is attached at one pole by thread, so as to allow the 
other to be above the surface of the mercury when the cup is 
filled, and have freedom of motion there ; a thick wire passes 
from the rod above down - perpendicularly, so as to dip a little 
way into the mercury of the cup ; it forms the connecting- wire, 
and the pole can move in any direction round it. When the 
connections are made with the pillar, and either of the wires 
from the stand-plates, the revolution of the wire, or pole above, 
takes place ; or if the wires be connected with the two coming 
from the plates, motion takes place in both cups at once.”-— 
Quarterly Journal, No, 28. p. 186. 
II. CHEMISTRY. 
10. Improvement cm Wedgwood's The difficulty 
of procuring clay, which contracts uniformly with heat, has 
M 2 
