- Electro-Magnetic and Galvanic Experiments. 145 
shewn fig. 3d. The cap O should be strong and if brass 
should be coated with the cement used in attaching it to the 
glass, (that used for nautical machines 1s best,) the gage may 
be attached to the cap, or enclosed in the receiver. 
The stiff wire, with the valve T and the ball U, may be 
entirely removed; and for it may be substituted a glass 
tube open at both ends cemented into the cock P, and 
reaching almost to the bottom of the globe. ‘The 
mercury, when it rises to the lower end of this tube, 
cuts off the communication with the receiver. This will 
perhaps be the simplest and best plan. It may be made 
a double pump by connecting the cap O with the barrel 
G, as on the dotted line 6— one valve opening in and one out. 
The weight of the mercury will be no objection as the ma- 
chine is small—the diameter of the globe about 4 inches, 
the height of the barrel about 8,.and the whole height to the 
plate R, 15 or 20 inches. ; 
Art. XITI].— brief account of some Electro-magnetic and 
Galvanic Experiments. By Rosert Hang, M. D. Pro- 
fessor of Chemistry in the University of Pennsylvania. 
Seven hundred feet of copper wire, nearly as thick as a 
knitting needle, were made to encircle the columns of the 
Lectnre Room. One end of the wire was connected with 
one end of a large calorimotor—the other, terminated in 
a cup of mercury—into this, a wire proceeding from the 
other pole of the calorimotor was introduced. Under these 
circumstances, a magnetic needle placed near the middle of 
the circuit, was powerfully affeeted—and whien the circuit 
was first interrupted, and then re-established by removing 
the wire from the cup, and introducing it again, the influ- 
ence appeared to reach the needle as quickly as if the cir- 
cuit had not exceeded seven inches in extent. ‘The needle 
being allowed to become stationary in the meridian, while 
the circuit was interrupted, and the end of the wire being 
then returned into the mercury, the deviation of the needle, 
and the contact of the wire with the metal, appeared per- 
fectly simultaneous. 
Vou. VIII. No. 1. 19 
