310 Experiments upon the Induction of Metallic Coils. 
induction of galvanic currents must be extremely small. T'wo rib- 
bons of zine well covered with silk, each eighty feet long and one inch 
in width, were wound together into a flat spiral, and the two ex- 
tremities of one were connected with a sensible galvanoscope. Up- 
on connecting the ends of the other with a calorimotor, containing 
twenty four square feet of zinc, no effect could be perceived upon 
the galvanoscope, while a bright spark was perceived upon breaking 
the connection of the other coil with the calorimotor. This experi- 
ment shews that galvanic induction must be very trifling, if after a 
current traverses a conductor eighty feet long, it would produce no 
effect perceptible by a galvanoscope in another conductor of the same 
length, wound into the same coil. Let Fig. 2. 
a, b, (fig. 2.) represent the extremities a 
of one coil, and c, d, the extremities of 
another, both of which are coiled into 
one flat spiral. If the extremities, a, , 
be connected with a sensible galvanos- 
cope, upon connecting the extremities c, 
d, with a powerful calorimotor no effect 
will be perceptible by the galvanoscope. 
Again, upon connecting the inner end of 
one ribbon b, with the outer end of the other c, by means a a cup 
of mercury, and connecting the other extremities of both ribbons 
with a calorimotor, the fluid thus running the same way in both 
ribbons, a much more vivid spark is obtained by breaking the con- 
tact at the cup of mercury than when only one ribbon was used. If 
the outer ends of both ribbons be connected with the cup of mer- 
cury, upon passing the current through this coil which thus passes 
in opposite directions in the adjacent layers, no spark whatever will 
be perceived upon breaking the contact. These experiments there- 
fore, appear to demenstinte; that adjacent currents running in the 
same direction, mutually conspire to increase the intensity of the 
effect, but when they run in opposite directions, they destroy it al- 
together. Part of the effect of a coil in increasing the intensity of 
the galvanic effect of a calorimotor, may be considered as owing to 
the length of the conductor, upon a principle not hitherto explained, 
and a part of its effect appears to be owing to the accumulation of 
the electric fluid in so small a space, whereby i its repulsive power is 
increased, and it is enabled to overcome greater obstacles than in 
peases. The effect appears to be similar to that of a small 
