330 Prof. Callan on the Induction Apparatus. 
which a condenser applied to the primary coil has on these cur- 
rents. 
The fifth defect is, that we cannot apply a Leyden jar or any 
condenser to the currents themselves. 
I have found that a core consisting of a coil of insulated or 
covered iron wire is free from all these defects. In such a core 
there is no complete circuit for any current in any section of the 
iron: for the electrical currents produced by the primary current 
in the sections of an enclosed iron coil move in the directions of 
the spirals of the coil; and since no spiral returns to itself, no 
current can return ,to the point where it originated. Neither 
does the current in any spiral of the coil oppose those in the 
adjoining spirals ; for the currents in all the spirals flow in the 
same direction, or in the direction of the primary current. 
Thirdly, since all the currents in the spirals of the iron coil 
flow in the same direction from the beginning to the end of the 
coil, they must unite and form one current, having an inten- 
sity equal to the sum of their intensities. This I have proved 
by using a coil of very fine insulated iron wire, about 10,000 feet 
in length, as the core of a copper coil. When the connexion 
between the ends of the copper coil and a single cell was broken, 
sparks about one-twelfth of an inch passed between the ends of 
the thin iron wire without using a condenser. Fourthly, by 
connecting the primary coil with a condenser, I have found 
that the intensity of the current in the core is increased as it is 
in the current of the secondary coil. Fifthly, by connecting the 
ends of the core or iron coil with a Leyden jar, the length of the 
spark is diminished and its brightness increased. The effect of 
the condenser on the currents in the core may assist us in under- 
standing the action of the condenser, which has not yet been 
satisfactorily explained. 
A core consisting of a coil of insulated iron wire, has not only 
the advantages of being free from the five defects to which all 
the cores in common use are subject, but it will also enable us to 
get electrical currents having at the same time great intensity 
and considerable quantity, and may therefore be very advanta- 
geous for working the Atlantic Telegraph, and for producing 
the electriclight. If we make a core of thirty covered iron wires, 
each one-eighth of an inch thick and 100 feet long, and wind over 
the iron coil a covered copper wire one-fourth of an inch thick, we 
can, with the aid of two cells and a suitable condenser, obtain 
thirty electrical currents, each having a considerable quantity of 
electricity, because the wires are short and thick, and an intensity 
greater than that which is required for the electric hight. Sixty 
covered iron wires, of the same length and thickness as those in 
the core, may be rolled on the copper coil. Another coil of cop- 
