Electro-physiology and electro-therapeutics : showing the best methods for the medical uses of electricity / By Alfred C. Garratt.

Iii 1831, Professor Henry, one of our American philosophers, was the first to discover this peculiar action of a long conductor when extended, and also, when coiled into a helix, as so modify- ing or increasing the current of a single galvanic pair at the moment when it ceases to flow. He was the first to employ coils of metallic ribbon for obtaining sparks and shocks from a single galvanic pair. By this means the brilliancy and power of the spark are very greatly increased whenever the circuit is broken. Thus far had this branch of science advanced when in the same year Professor Faraday, of England, discovered that an electric current, as well as a magnet, is able by induction to develop elec- tric currents in conducting wires. This he proved by placing on an insiilating plane two parallel conducting wires very near to each other, but without touching. The two ends of one of these wires are connected with the poles of a galvanic battery, so that it in fact becomes the connecting wire between the two poles of that battery. The two ends of the other wire are con- nected with the extremities of a sensitive galvanometer, simply to judge of the electric movement in this wire, if any, by the deviations of the needle of the instrument. At the moment the battery current commenced to flow through the first wire, the needle of the instrument is seen to deviate at first, then to quiver and oscillate, and finally to come back to an equilibrium, which remains at zero, just as it was before the current was let on the first wire; and thus it remains undisturbed as long as the current of the battery continues to traverse the neighboring wire; but the instant the current is interrupted in the first wire, the needle suffers another deflection, and this in a con- trary direction to that which occurred at the closure of the current. Thus he proved that the galvanic current which coiirses through the one wire, determines an instantaneous but opposite current in the other wire at the moment when it begins to flow, and another equally instantaneous reverse current at the moment when it ceases. Dr. Faraday was led to suppose, from the manifest analogy existing between the properties of ?nagnets and those of electro- dynamic coils or cylinders, that the same results would be obtained