Prof. Callan on the Induction Apparatus. 333 
house’s coils, would, I think, answer better than his for the 
Atlantic Telegraph. 
It appears to me that Mr. Whitehouse’s coils admit of three 
important improvements. First, they may be greatly improved 
in the core by substituting for his secondary coil of copper wire 
a coil of covered iron ‘wire of the same length and thickness. 
The iron wire would be intensely magnetized by the primary 
current, and by the inductive magnetic power of the enclosed 
iron bar; and in losing its magnetism at the moment the battery 
connexion is broken, a current will be induced in it of far greater 
intensity than that of the secondary current in Mr, Whitehouse’s 
coil. Mr. Whitehouse’s object in connecting the ends of one 
core with the ends of another by iron armatures, is to prevent 
the rapid suspension of the magnetic power of the cores at the 
moment the connexion between the battery and primary coil is 
broken. By causing the cores to lose their magnetism gradu- 
ally, a series of currents corresponding to the successive diminu- 
tions of magnetic power is induced in the secondary coil: this 
series of currents has the effect of a continuous current, which is 
found to be of use in working the telegraph. The same object 
may be attained by using a core consisting of an iron bar and a 
coil of insulated iron wire. The iron bars may be connected by 
iron armatures extending over the ends of the iron coils, but 
separated from them by a piece of gutta-percha about the one- 
fortieth of an inch in thickness. Mr. Whitehouse’s object might 
perhaps be attained still better by connecting the cores of every 
two coils, by six or seven, or a greater number of armatures. 
This may be done by brazing or otherwise fastening to the iron 
bar in each coil, plates of iron about a quarter or three-eighths 
of an inch thick, and sufficiently large to project an inch or two 
beyond the iron coil of the core. A small piece should be cut 
out of each plate, that the primary wire may pass from one side 
of the plate to the other. The corresponding plates fastened to 
the two iron bars may be connected by a plate of iron. Thus the 
two iron bars will have as many armatures as iron plates, and the 
magnetic power of the core will be retained longer than if there 
be only two armatures, and consequently the series of induced 
currents will continue for a longer time. Secondly, a great im- 
provement may be made in the primary coil. Mr. Whitehouse’s 
primary coil consists of twenty-four copper wires, No. 14, or 
about the ;+;th of an inch thick, and 100 feet long. Now if the 
primary coil were made of copper wire of the same length, and 
nearly half an inch thick, it would conduct as much electricity 
as the twenty-four wires used by Mr. Whitehouse, and would 
produce greater magnetic power in the core, because the elec- 
tricity flowing in the thick wire would be nearer to the core than 
