188 
MR. GASSIOT ON THE POSSIBILITY OF OBTAINING A SPARK 
ing screws were attached for the purpose of making connexions with the voltaic bat- 
tery, the whole forming an electro-magnet of considerable power. Over this thick 
wire 2268 feet of No. 30 copper wire, also well covered with cotton, were wound 
round, the ends being attached to separate binding screws, and forming a secondary 
coil. A bar of soft iron was placed so as to rotate within about ^ 0 th of an inch from 
the ends of the iron wires, which ends were previously ground quite smooth, so as to 
expose an even surface ; and connexions were made from the primary wire by means 
of two cups of mercury, so that the contact with the voltaic battery should be made 
and broken at every revolution of the iron bar. 
The apparatus when in action is represented by fig. 3, and may be described as 
follows. A represents the iron wires forming the electro-magnet when the voltaic 
Fig. 3. 
current is passed through the primary coil ; C, C the secondary coil ; D the bar of 
soft iron ; E, E cups of mercury connected with the primary coil ; F, F binding screws 
to connect the primary coil with the voltaic battery ; G, G binding screws attached to 
the ends of the secondary wire. Slips of copper are attached to the bar D, so that 
when the bar rotates the connexion of the mercury cups, E, E, with the primary coil, 
and consequently with the voltaic battery, is made and broken at every revolution. 
The weight of the iron wires is about 8 lbs., the primary coil about 4^ lbs., and of the 
secondary wire about 1 lb. The entire apparatus is mounted on a strong wooden 
base. 
23. On making connexion with the primary wire, by the binding screws F, F, to a 
series of twenty of the constant battery large cells ( 1 7 -), the bundle of iron wires 
