DOVE ON THE ELECTRICITY OF INDUCTION. 131 



very slight shock was perceived. The same takes place with 

 tubes of sheet iron. Enclosing spirals of copper wire, which 

 surround the spirals, have a similar influence in all these experi- 

 ments to cut brass tubes w^hen the ends of the spirals are un- 

 connected, but they act on the contrary as entire tubes when 

 their ends are connected. 



Although the parallelism of the secondary current and the 

 extra current cannot be traced further, yet it may be permitted 

 to assume it for the galvanometric test, for, as will be shown 

 hereafter, complete correspondence can be proved to exist 

 between both currents for the induced current of the Ley- 

 den jar. 



II. Currents induced by the evanescent magnetism of electro- 

 magnetized rods of iron and bundles of wires, when the 

 current magnetizing them is that of a thermo-battery or 

 thermo-pile. 



37- If the poles of the thermo-battery described above (6) are 

 united by a powerful electro-magnet with wire 2~ lines in thick- 

 ness, sparks are perceived on breaking the circuit, as when con- 

 nexion is made by a flat spiral of sheet copper; at the same 

 time the horseshoe attracts the keeper very decidedly. If the 

 handles attached to the ends of the induction-spirals which 'sur- 

 round the electro-magnet are grasped in the hands previously 

 moistened, a shock is perceived on breaking the circuit or pile. 

 The shock of a bundle of wires disappears if it is enclosed in 

 an entire brass tube. On the contraiy, the galvanometric ac- 

 tion is in both cases alike. The shock appears here likewise 

 more intense when the break quickly follows the closing of the 

 circuit. 



38. The shock on breaking the circuit in a direct manner by 

 means of a connecting wire of sheet copper forming a flat spiral ^ 

 is perceptible when the discharge is effected by platinum spa- 

 tulas through the tongue, and is very much increased by the in- 

 sertion of bundles of wires. This last increase of power could 

 not be perceived in the discharges of a battery with smaller ele- 

 ments, having the dimensions of one of Nobili's piles for mea- 

 suring the conduction of heat. 



The current induced by the connecting wire of a thermo-bat- 



