PHILOSOPHICAL SOCIETY OF WASHINGTON. 263 



feet of zinc surface was principally used ; and the galvanic cir- 

 -cuit was interrupted by drawing one end of the copper ribbon or 

 wire over a rasp in good metallic contact with the other pole of 

 the battery. 



From the energetic action of the flat ribbon coil in producing 

 the induction of a current on itself, it was inferred that the sec- 

 ondary current would also be best induced by it. With the sin- 

 gle larger ribbon coil in connection with the battery, and another 

 ribbon coil placed over it resting on an interposed glass plate, 

 at every interruption of the primary circuit, an induction spark 

 was obtained at the rubbed ends of the second coil ; though the 

 shock was feeble. With a double wire spool (one within the 

 ■other) of 2650 yards, placed above the primary coil (having about 

 the same weight as the copper ribbon) the magnetizing effects 

 disappeared, the sparks were much smaller, " but the shock was 

 almost too intense to be received with impunity." The secondary 

 current in this case was one of small "quantity" but of great 

 " intensity." With a single break of circuit in the primary, it 

 was passed through a circle of 56 students of his senior class, 

 with the efl'ect of a moderate charge from a Leyden jar. From 

 various experiments, the limit of efficient length for a given gal- 

 vanic power was ascertained ; beyond which the induced current 

 was diminished. Employing a Cruickshank battery of 60 small 

 elements (4 inches square) he found with the ribbon coil that the 

 induced currents were exceedingly feeble, but with the long wire 

 helix as the primary circuit that strong indications were produced. 

 By the alternations of the ribbon and wire coils, the fact was 

 established "that an intensity current can induce one of quantity, 

 and by the preceding experiments the converse has also been 

 shown that a quantity current can induce one of intensity ;" a 

 result which has had an important bearing on the subsequent 

 development of the electro-magnetic " Induction-Coil." With a 

 long ribbon coil receiving the galvanic current from 35 feet of 

 zinc surface, sensible induction shocks could be felt from a large 

 annular coil of four feet diameter (containing five miles of wire) 

 when placed in parallelism at a distance of four feet from the pri- 

 mary coil: while at the distance of one foot the shock became 

 too severe to be taken. With this arrangement an induction 

 shock was given from one apartment to another, through the 

 intervening partition. 



Successive orders of Induction. — When it is considered that 

 the primary current in such eases has a considerable duration, 

 while the secondary current is but momentary, being developed 

 only at the instant of change in the primary, it could certainly 

 not have been expected that this single instantaneous electrical 

 impulse of reaction would be capable of acting as a primary 

 current, and of similarly inducing an action on a third independ- 



37 



