BEFORE COMPLETION OF THE VOLTAIC CIRCUIT. 
189 
becomes intensely magnetic, and the bar D rotates with great rapidity. Copper wires 
attached to the secondary coil by the screws G, G, are connected with the pillars of 
the micrometer electrometer ( 12 .) ; and when the platinum points or plates of this 
instrument are approximated to ^th of an inch, a minute but brilliant spark ap- 
pears at every revolution of the bar. 
24. When the pillars of the micrometer electrometer ( 12 .) were separated three or 
four inches, the spark could be taken by the knuckle, or by a metallic ball, from 
either of the balls attached to the pillars, which then became the terminations of the 
secondary coil ; and a Leyden jar was charged sufficient to deflect the leaves of a 
gold-leaf electroscope. 
25. On introducing an extremely delicate Harris’s thermo-electrometer in the 
current of the secondary wire, the liquid rose 3°. 
26. A voltameter filled with water slightly acidulated with sulphuric acid, was in- 
troduced in the secondary circuit, and the gases were evolved in minute bubbles as 
the bar rotated ; and when charcoal points were attached to the terminations of the 
secondary coil, and these were approximated by means of the micrometer electro- 
meter ( 1 . 2 .) to within 555 th of an inch, the sparks appeared in such quick succession 
while the armature rotated, as to have the appearance of a continued but glim- 
mering flame. 
27. Thin paper introduced between the platinum or charcoal terminals, was per- 
forated at every revolution of the bar, but no increase of distance in the spark could be 
obtained through the vacuum obtained bp means of a good air-pump. 
28. In the preceding experiments I had obtained most of the usual results, which 
are generally denominated intensity effects: the spark (23.) ; charge of a Leyden jar 
(24.) ; heating power (25.) ; chemical action (26.). In respect to the shock, it was 
most intense. One revolution of the bar, when the hands were in contact with the 
terminations of the secondary wire, created a most painful sensation. On two occa- 
sions I inadvertently touched both wires, the armature making three or four revolu- 
tions ; the pain was so intense that I suffered from the effects for a considerable time 
afterwards ; but as this effect, as is well known to all who have experimented with 
the secondary coil, is so much increased by the introduction of iron wires in the helix, 
I repeated the experiments under rather different circumstances, viz. by avoiding the 
use of this metal. 
29. For this purpose the apparatus ( 22 .) was 
removed, and a helix composed of 150 feet of 
No. 18 copper wire, covered with cotton, formed 
the primary, and 2100 feet of No. 26, similarly 
insulated, formed the secondary, the whole 
wound round a hollow cylinder of wood. Fig. 4. 
represents the form of the coil ; C the coil, the 
shaded part representing the primary, and the 
Fig. 4. 
