Prof. Callan on the Induction Apparatus. 325 
form of core which has five advantages over the cores in common 
use, which will enable us to get intensity and quantity currents, 
and may therefore answer for the Atlantic Telegraph and for the 
electric light ; fourthly, an improved method of insulating the 
secondary coil; fifthly, a contact-breaker in which the striking 
parts are copper, and which acts as well as if they were platina ; 
sixthly, an explanation of the action of the condenser, which 
appears to me more satisfactory than any other I have seen ; 
lastly, some new facts regarding the condenser, and an improved 
method of making it. 
The first result is a means of obtaining, not from a coil sur- 
rounding the armature of a magnet, but from the armature itself, 
a voltaic current capable of giving a shock. This result is ob- 
tained by making a coil of fine insulated iron wire, and an elec- 
tro-magnet of such a form that the coil will fit between its poles. 
The iron coil is then the armature of the magnet. If the helix of 
the electro-magnet be connected with a battery, the iron becomes 
magnetized ; and on account of its proximity to the magnetized 
iron, the coil of iron wire, or the armature of the electro-magnet, 
will be also magnetized, and will lose its magnetism when the 
connexion between the battery and electro-magnet is broken, or 
when the electro-magnet is demagnetized. If, at the moment 
the iron coil loses its magnetism, the ends of it be held in the 
hands, a shock will be felt. If the ends of the iron coil be con- 
nected with a delicate galvanometer, the needle will be deflected 
at the moment the coil is magnetized by the electro-magnet. 
Hence at the moment of magnetization or demagnetization, an 
electric current is produced in each section of the iron at right 
angles to its magnetic axis. From this, two inferences may be 
drawn ,—first, that if for the copper coils used in magnetic tele- 
graphs, coils of iron wire were substituted, electrical currents of 
greater intensity might be obtained ; secondly, that if iron wire 
were used in the secondary coil of induction coils, the intensity 
of the secondary currents would be increased. 
Here I shall take occasion to explain the causes which produce 
the secondary current in the induction coil. I believe that this 
current is the result of the combined action of three inductive 
forces ; one arising from the sudden cessation or destruction of 
the magnetism of the core, the second from the cessation of the 
magnetism of the primary coil, and the third from the destruc- 
tion of the magnetism of the secondary coil at the moment the 
connexion between the battery and primary coil is broken. This 
supposes, first, that as long as the primary coil is connected with 
the battery, magnetic power is given, not only to the iron core, 
but also to the primary and secondary coils ; and secondly, that 
in each of them, at the moment of losing its magnetism, an electric 
