36 M. Matteucci on iJi€ Electric Discharge of the Jar, 



Vfith an insulating handle, at a certain distance from the con- 

 ductor or the boiler, whilst the other extremity of the wire 

 was in contact with the boiler or the conductor, there was 

 always a constant deviation in the needle, but it was less, how- 

 ever, than that which existed when there was no interruption 

 in the circuit. In this case, even at the distance of several 

 centimetres, there was a series of sparks which appeared 

 without interruption. I wished however to assure myself of 

 it by one of the very ingenious means discovered by Mr. 

 Wheatstone. This was a revolving disc, upon which I traced 

 black stripes. The space of time which elapsed in passing 

 from one stripe to the other was 0*00009 of a second : the disc 

 appeared immoveable. It is proved therefore that the light 

 was not continuous, and that it was a series of sparks or of 

 successive discharges which traversed the circuit, giving to 

 this circuit itself the properties of a conductor traversed by a 

 voltaic current. The enormous quantity of electricity which 

 is produced by this machine in all circumstances of the atmo- 

 sphere, allowed of my making a series of experiments which 

 complete the identification of the electric current properly so 

 called with the discharge of the jar. I prepared a demi-right 

 angle of copper wire perTectly similar to the moveable conductor 

 of Ampere, The two small cups filled with mercury, into 

 which the points of the moveable conductor are plunged, are 

 fixed on a column of resin. The moveable conductor is sup- 

 ported by a silk thread without torsion. I fixed upon a resin 

 foot a copper wire, which was consequently parallel to the 

 longest side of the right angle, to which it could thus be 

 brought near or removed from it at will. The whole appa- 

 ratus was covered with a bell glass to prevent the effect of the 

 agitation of the air. It is not difficult to conceive the ar- 

 rangements of the experiment so as to cause the discharge of 

 a battery to pass into the two conductors, either in the same 

 direction, or in the opposite one ; I shall therefore not stop to 

 describe them. I began by passing the discharge into one 

 only of the conductors, keeping the other either insulated or in 

 communication with the ground : one while the discharge 

 passed through the moveable conductor, at another by the 

 fixed conductor. When the two conductors are at the distance 

 of fifteen to twenty millimetres, employing the discharge of a 

 battery of nine jars, each of which had a surface of 0'"*'''*12, no • 

 movement was observed in the moveable conductor, even when 

 examined with the telescope of the cathetometer. At a di- 

 stance less than fifteen millimetres between the two conductors, 

 the moveable wire was in all cases seen to be slightly attracted 

 by the fixed conductor. This same attraction is manifested in 



