310 Experiments upon the Induction of Metallic Coils. 



induction of galvanic currents must be extremely small. Two rib- 

 bons of zinc well covered with silk, each eighty feet long and one inch 

 in width, were wound together into a fiat 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. 3. 



a, b, (fig. 2.) represent the extremities 

 of one coil, and c, d, the extremities of 

 another, both of which are coiled into 

 one flat spiral. If the extremities, a, b, 

 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 of 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 demonstrate, 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- 

 too-ether. 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 its repulsive power is 

 increased, and it is enabled to overcome greater obstacles than in 

 ordinary cases. The effect appears to be similar to that of a small 



