THE FULGTJEATOR. 
105 
These jars are mounted vertically on insulating glass pillars, 
three feet high, and the charging wires are bent down on the outsides 
into a position which enables the nob of each jar to come into 
contact with the coating of its neighbour. All the insulating 
pillars are fixed in a frame in such a way as to permit them to 
turn on their vertical axes, and are connected at the foot by levers 
with a long sliding-bar, which moves them simultaneously, as in 
the arrangement before described. The only points of difference 
between the present and former arrangement are in the self-acting 
contrivances for dis-severing the jars from their battery connection 
with each other, and from conducting communication with the 
electrical machine, and in the vertical position of the jars, the 
former arrangement having had the jars placed horizontally. This 
vertical arrangement was adopted principally for economy of space, 
and to accommodate the apparatus to the size of the room in which 
it was used. 
It now measures 12 feet in length by six feet in height. Un- 
fortunately, this only gives a space of about four and a half inches 
between each jar, and consequently the length of spark obtained 
from it does not exceed four feet six inches. In attempting to 
obtain longer sparks, the discharge takes place across the intervals 
from jar to jar. 
There can be but very little doubt, however, that if the jars 
were placed further apart, sparks of nearly double this length 
could be obtained. On one occasion, when attempting to get longer 
sparks, the discharge passed down over the insulators of the dis- 
charger, which were each three feet in length, and completed the 
circuit across from one to the other on the floor beneath the carpet, 
the entire length being nearly 12 feet; thus showing the power 
which semi-conducting surfaces possess to help on an electrical 
discharge over a greater distance than it could leap in free 
air. 
Great caution was also required in manipulating with the appa- 
ratus, the operator being obliged to work the sliding bar with 
a long insulating handle, as some rather unpleasant shocks were 
received even at a distance of two or three feet. 
The power of rarefied air to increase the length of a luminous 
discharge is beautifully shewn by the arrangement of 63 double- 
wick spirit lamps placed in a straight line, with their 126 flames 
touching so as to form a continuous line of flame nine feet in 
