380 Electro-Magnetic Experiments. 
A convenient apparatus for this dig- 
ital experiment consists of two copper 
wires coiled at one end into a close 
flat spiral C and bent at the other end 
P at right angles downward. The 
coils being placed flat on the table 
with the disc of antimony A between 
them and the bent ends in the mercury cups of the galvanometer, the 
apparatus is ready for experiment. 
4. With one fourth of a grain of antimony between two straight 
wires the needle was deflected 22° upon the application of the fin- 
gers. 
5. A piece of copper wire one sixteenth of an inch in diameter 
‘and 2 inches long being laid with its ends across the copper wires 
(the poles or termination of the coil of the instrument) and one of 
the junctures pressed between the thumb and finger the needle was 
deflected 6 degrees. | 
Ihave constructed an electro-magnetic multiplier upon the plan 
of Schweigger with 120 coils within one inch of the needle above 
and below it. It is affected by water; but not by the thermo-elec- 
tricity produced by animal heat. 
I have also constructed a dip- 
ping ring. It isa coil of about 
40 turns in a circle of 53 inches 
in diameter. ‘The ends of this 
coil terminate in two brass pivots 
diametrically opposite to each 
other. ‘These pivots which are 
small, roll on two horizontal 
straight edges and have their ex- 
treme ends, which are amalga- 
mated running in mercury con- 
tained in little copper troughs. ‘The mercury rises, by its tendency 
to form a globule, above the trough which contains it, thus uniting 
itself to the pivot which isstraight. ‘The ring being nicely balanced 
like a dip needle, and a current of electricity sent through it, by 
bringing the poles of the galvanometer into the mercury troughs, 
will turn on the pivots till its plane is perpendicular to the axis of the 
true dip of the place. It is difficult to make the pivots so true that 
the ring will turn at once into the plane unless we go to the expense 
