328 Prof. Callan on the Induction Apparatus. 
that at present the length of the secondary coil is nearly 50,000 
feet. Since the increased length of wire was put on the coil, I 
have got from it, with a single cell, 6 inches by 4, and without a 
condenser, sparks +3ths of an inch in length. I expect that 
with the same battery it will give sparks at least an inch long 
without a condenser. This is, I believe, the most powerful coil 
ever made. 
The second result is, that if a bundle of iron wire be put into 
a coil of insulated thick copper wire connected with a battery, 
the quantity of electricity which will flow through another coil 
in contact with the same battery, will be considerably greater 
when the iron wires are in the first coil than when they are 
altogether or partly removed. This I found by using a eontact- 
breaker worked by an electro-magnet, the helix of which was 
connected with the same battery by which an induction coil was 
excited. In trying the effect of the induction coil without an 
iron core in its primary coil, I found that the action of the elec- 
tro-magnet of the contact-breaker was slow and feeble. When 
a few wires were put into the primary coil, the action of the 
contact-breaker was sensibly increased ; and when the primary 
coil was filled or nearly filled with wire, the attraction of the 
electro-magnet became considerably stronger, and consequently 
the voltaic current flowing round it must have been considerably 
increased. Since the core of the induction coil increases the 
quantity of electricity flowing from the battery through the helix 
of the electro-magnet, we must suppose that the iron of the 
magnet reciprocally increases the quantity of electricity trans- 
mitted through the primary coil, and that therefore little or no 
battery power is lost by usmg an electro-magnet for making and 
breaking contact, instead of the magnetized core of the coil. 
Hence it appears also to follow, that a secondary current of greater 
intensity may be got with a battery of given power from a great 
number of small coils than from one large one, in which the 
conducting power of the primary coil is equal to the sum of the 
conducting powers of the primary wires of all the small coils; 
for the magnetic power of the core of each of the small coils will 
be increased by the magnetism of the cores of the others. 
The third result is a form of core which has five advantages 
over all the cores in common use, and which may enable us to 
get electrical currents having at the same time great intensity 
and considerable quantity, and may therefore be very useful for 
working the Atlantic Telegraph, and for producing the electric 
light. In my experiments on the core, I have used cores of six 
different forms, and varying in weight from one pound to two 
hundred and a half of iron wire. I have used, first, a core of 
uninsulated iron wire coiled on an ivon bar ; secondly, the ordi- 
