228 Royal Institution. 



rent of the battery Avas to be sent ; the other was that in which the 

 secondary current was to be aroused. The ends of the latter were 

 connected by wires with a third spiral placed at a distance, so that 

 when the secondary current was excited it passes through the third 

 spiral. Underneath the latter, and sejiarated from it by a sheet of 

 varnished glass, was a fourth spiral, whose two ends were connected 

 with the universal discharger, between the knobs of which a quantity 

 of gun-cotton was placed. When the battery was discharged 

 through the first spiral, a secondary current was aroused in the 

 second spiral, which completed its circuit by passing through the 

 third spiral : here the secondary acted upon the spiral underneath, 

 developed a tertiary current which was sufficiently strong to pass 

 between the knobs, and to ignite the gun-cotton in its passage. It 

 was shown that we might proceed in this way and cause the tertiary 

 to excite a current of the fourth order, the latter a current of the 

 fifth order, and so on ; these children, grandchildren, and great 

 grandchildren of the primary being capable of producing all the 

 eifects of their wonderful progenitor. 



'i'he phsenomena of the extra current, which exists for an instant 

 contemporaneously with the ordinary current in a common voltaic 

 spiral, were next exhibited ; and the question whether a spiral through 

 which a Leyden battery was discharged exhibited any similar 

 phsenomena, was submitted to examination. It was proved, that the 

 electric discharge depended upon the shape of the circuit through 

 which it passed : when two portions of such a circuit are brought 

 near each other, so that the positive electricity passes in the same 

 direction through both of them, the effect is that the discharge is 

 weaker than if sent through a straight wire ; if, on the contrary, the 

 current flow through both portions in opposite directions, the 

 discharge is stronger than if it had passed through a straight wire. 

 A flat spiral was taken, containing 75 feet of copper wire; one end 

 of the spiral was connected with a knob of the universal discharger, 

 and the other knob was connected with the earth: between the knobs 

 of the discharger about 4 inches of platinum wire were stretched; 

 on connecting the other end of the spiral with the battery, a discharge 

 passed through it of such a strength that it was quite unable to 

 raise the platinum wire to the faintest glow. The same length of 

 copper wire was then bent to and fro in a zigzag manner, so that on 

 every two adjacent legs of the zigzag the current from the battery 

 flowed in opposite directions. When these 75 feet of wire were 

 interposed between the battery and the platinum wire, a discharge 

 precisely equal to that used in the former instance, raised the plati- 

 num wire to a high state of incandescence, and indeed could be 

 made to destro)^ it altogether. 



When a primary and a secondary spiral are placed opposite to 

 each other, a peculiar reaction of the secondary upon the primary 

 is observed. If the ends of a secondary (50 feet long) be connected 

 by a thick wire, the eff"ect upon the primary current is the same as 

 when the ends of the secondary remain wholly unconnected. If 

 the ends of the secondary be joined by a long thin platinum wire, 

 the reaction of the secondary is such as to enfeeble the primary. 



