104 
JOUKNAL OF THE PLYMOUTH INSTITUTION. 
Ey this means I was able to place them first in a position which 
permitted them to be charged all together as a battery. When 
charged, the connecting conductors were removed, thus leaving 
each jar as a separate charged element. 
By a simple motion of the sliding bar, the whole of the jars were 
simultaneously brought round into consecutive arrangement, each 
jar having its nob in contact with the coating of the next. Two 
insulated balls, one placed at either end of the apparatus, served 
as terminals to connect the coating of the last with the nob of 
the first, the circuit being completed across the nobs of a suitable 
universal discharger previously connected with these terminals. By 
this means sparks of two feet in length were easily procured from 
a dozen pint Leyden jars. 
There has been of late a growing mania for the production of 
long electrical sparks among electricians, which received its first 
impulse when I exhibited the efi'ects of tension of my new arrange- 
ment of induction coil, which I exhibited to the Plymouth Insti- 
tution in 1856, and for which I was subsequently honoured with 
a silver medal from the Royal Cornwall Polytechnic Institution. 
Prom the secondary coils of these instruments I obtained sparks 
of from three to five inches in length. 
These exalted efi'ects gave an impetus to the subject in all 
countries. Ritchie, in America, constructed a large apparatus 
which gave sparks 12 inches in length. Rhumkorf, of Paris, the 
originator of the intensity coil, whose machines had only hitherto 
given sparks half an inch in length, greatly improved their con- 
struction, and Siemans produced one at the Great Exhibition of 
1862 which gave sparks over two feet in length. Lately a gigantic 
machine has been constructed for the Royal Polytechnic Insti- 
tution, London, under Professor Pepper's direction, by Mr. Apps. 
According to calculation this should have given sparks 10 or 12 
feet long, but the longest yet obtained have been only 30 inches. 
Last year a scientific amateur, to whom I had shewn my intensity 
arrrangement of Leyden jars, expressed a desire to extend the prin- 
ciple, and requested me to prepare for him a much larger set of 
apparatus. I accordingly constructed for him the instrument now 
before the society. It consisted of fifteen (now thirteen) Leyden 
jars, each two feet high and four and a half inches diameter, 
coated one foot high ; each jar therefore contains a square foot of 
surface. 
