Prof. Callan on the Induction Apparatus. 323 
nitric acid diluted with its own volume of water. Into the 
nitric acid were poured alternately small quantities of a solution 
of nitrate of silver and of hydrochloric acid, the object being to 
cause the chloride of silver to form in a minutely divided state, 
so as to produce a milky liquid, into the interior of which the 
brilliant converging cone of light might pass, and the currents 
generated in the flask by the heat, might drift all the chloride 
successively through the light. The chloride, if otherwise ex- 
posed to the sun, merely blackens upon the surface, the interior 
parts undergoing no change; this difficulty I hoped therefore to 
avoid. The burning-glass promptly brings on a decomposition 
of the salt, evolving on the one hand chlorine, and disengaging 
a metal on the other. In one experiment the exposure lasted 
from 11 a.m. to 1 p.m.; it was therefore equal to a continuous 
midday sun of seventy-two hours. The metal was disengaged 
very well. But what is it? It cannot be silver, since nitric 
acid has no action upon it. It burnished in an agate mortar, 
but its reflexion is not like the reflexion of silver: it 1s yellower. 
The light must therefore have so transmuted the original silver 
as to enable it to exist in the presence of nitric acid. In 1837 
I published some experiments on the nature of this decomposi- 
tion in the Journal of the Franklin Institute. 
Though this experiment, and several modifications of it which 
I might relate, fail to establish any permanent change in the 
metal under trial in the sense of an actual transmutation, it does 
not follow that we should despair of a final success. It is 
not likely that Nature has made fifty elementary substances of 
a metallic form, many of them so closely resembling one another 
as to be with difficulty distinguished; moreover, chlorine and 
other elementary substances can be changed by the sunlight im 
some respects permanently; and if silver has not thus far been 
transmuted into a more noble metal, as platinum or gold, it has 
at all events been made transiently into a something which 
is not silver. Those who will reflect a little on the matter, can- 
not fail to observe that the sun-rays really possess many of the 
powers once fabulously imputed to the powder of projection and 
the philosopher’s stone. 
XXXVIII. On the Induction Apparatus. By the Rev. N. J. 
Catian, D.D., Professor of Natural Philosophy in the Roman 
Catholic College, Maynooth*. 
; A is now more than twenty years since I discovered the 
method of making the induction coil, or a coil by which an 
electric current of enormous intensity may be produced with the 
* Communicated by the Author. 
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