Prof. Callan on the Induction Apparatus. 331 
per wire, one-fourth of an inch thick, may be put over the second 
iron one, and over this copper coil we may wind sixty or eighty 
covered iron wires, each 100 feet long and one-eighth of an inch 
thick. Then the innermost iron coil will be the core of the first 
copper one; the second iron coil will be the secondary coil of the 
first copper coil, and the core of the second; the third iron coil 
will be the secondary coil of the second copper coil. Ifthe copper 
wires be connected with a battery of six cells, each about 5 inches 
square, and a condenser of sufficient size, an enormous magnetic 
power will be given to the 150 or 170 wires of the iron coils ; 
and consequently 150 or 170 electric currents of considerable 
quantity and intensity will be produced as often as the connexion 
between the copper wires and the battery is broken. If neces- 
sary, the number of iron coils, and therefore the number of elec- 
tric currents, may be increased. Mr. Shephard has got a bril- 
liant electric light from eighty electric currents produced in coils 
of copper wire on the armatures of permanent magnets. I think 
that 150 currents produced by the coil I have described would 
far exceed in quantity and intensity the eighty currents obtained 
from Mr. Shephard’s machine. 
The electric light may perhaps be produced by several coils, 
like the one I showed at the meeting of the Association, and 
which has given sparks the 14th of an inch, with one cell and 
without a condenser. The secondary coil is divided into four 
parts, each of which will give sparks about a quarter of an inch. 
I intend to make four or five other coils of equal power, and to 
divide the secondary coil of each into six or eight parts. The 
ends of the wire of each part will be left projecting from the 
coil. Thus in the five or six coils there will be between thirty 
and forty small secondary coils, each containing about 8000 or 
10,000 feet of fine iron wire. Hach of these secondary coils 
will give sparks at least one-eighth of an inch, with a battery 
of five or six cells and without a condenser. With a good con- 
denser we may fairly expect that each will give sparks nearly 2 
inches in length. Thus with a battery of five or six ‘cells I 
think I shall have between thirty and forty currents, each capable 
of passing through about 2 inches of air. If the opposite ends 
of the thirty or forty small coils be connected with the opposite 
coatings of several large Leyden jars, and the sparks be passed 
between two coke-points, a brilliant light may be produced. 
Besides the coil which I have described, and which was divided 
into four parts, I made another which was 40 inches long, was 
divided into nine parts, and in which there were at least 70,000 
feet of fine iron wire. Unfortunately, the secondary coil was seri- 
ously injured before I was able to make a single trial of its power. 
In dividing the two coils into several parts, I had three objects 
