198 
J5XP£imiENTS IN ELECTRICITY. 
V. 
Experiments in Electricity. By Mr. T. Howloy. 
To Mr. Nicholson. 
SIR, 
I N consequence of repeating and varying an experiment 
descrihed in Cavallo’s Complete Treatise on Electricity^*", 
I discovered, about four years ago, the followitig experiments, 
xvliich, 1 have reason to think, are by no means generally known 
to electricians, and therefore an account of them may possibly 
deserve to be recorded In your excellent Journal. 
The apparatus employed in pet forming them w'ere simply 
two pith-balls and a nanow piece of wood eight indies long, 
having in the middle of one of its surfaces a small groove 
extending its whole length. The pith-balls were three- 
eighths of an inch in diameter, and the groove was fitted, as 
nearly as it could be, to their curvature, its depth being half 
the diameter of the balls. After a jar, containing about l68 
square inches of coated surface had been placed at the prime 
conductor of the electrical machine, and one extremitv of the 
universal discharger had been connected with its outside, the 
piece of wood was insulated upon the table of that instrument, 
the extremities of the opposite wires of which, without their 
balls, were placed at 4^ inches distance from each other in the 
groove ; the w'ires being so adjusted as to lie nearly parallel 
with its bottom, but without touching that or its sides. The 
charge communicated to the jar was not, in any case, so strong 
as to be capable of exploding over the interval in the ciicuit; 
but, on the contrary, was always much w’eaker ■, and though 
this observation does not define its strength with precision, yet 
it will enable the electrician, who is desirous of repeating the 
experiments, to ascertain, by one or two trials, a charge which 
will produce the intended effects ; it may not be improper to 
add, that the mode of discharging the jar was by bringing one 
* Vol. I, p. V09, Fourth Edition. 
ball 
