632 London Electrical Society. 
argument in favour cf the theory ; though it must be allowed that, in 
the effort to extend the knowledge of any subject, there is a tendency 
in different minds to adopt the same errors respecting it, as well as 
the same truths ; a fact of which we have seen other examples in the 
course of the present article. 
According to M. Neumann (Ibid. p. 454), the ‘ third ray,” not 
being perceived as light, must manifest its existence as radiant heat, 
or as a chemical power, or as some other agent [“ als strahlende 
Wirme, oder chemisch wirkend, oder als irgend ein anderes Agens’’), 
and he thinks that the nature of this ray will be more easily investi- 
gated, if the laws of reflexion shall be deduced from the aforesaid 
theory. But we have seen that the laws of reflexion are, to all ap- 
pearance, at variance with the theory, and they take no account 
whatever of the third ray. Besides, the discoveries which have been 
made of late years respecting the polarization of radiant heat, and 
the strong analogies that have been traced between it and light, 
amount to a demonstration that its vibrations are transversal, and of 
course essentially different from those of the supposed third ray, 
which are normal, or nearly so. There is every reason to believe 
that the vibrations of the chemical rays are also transversal; and 
we may confidently assert, that the three species of rays—those 
of light and heat, and the chemical rays,—are produced not only 
by vibrations of the same medium, but by the same kind of vibrations, 
propagated with nearly the same velocities. If, therefore, the third 
ray of MM. Cauchy and Neumann has any existence, it must be re- 
ferred to ‘‘some other agent,” the nature of which it is impossible 
to conjecture. 
Enough has now been said to show that the optical theory which 
we have examined, and which has passed current in the scientific 
world for a considerable period, is quite inadquate to explain the 
leading phenomena of light, and that it is based upon principles 
which are altogether inapplicable to the subject. M. Cauchy states, 
in the memoir so often quoted (Mém. de l'Institut, tom. x. p. 294), 
that the first application which he had made of his principles was 
to the theory of sound, and that the formulas which he had deduced 
from them agreed remarkably well with the experiments of Savart 
and others on the vibrations of elastic solids. AsI have already in- 
timated, it is in the solution of such questions (which, however, have 
long been familiar to mathematicians) that the fundamental equa- 
tions of M. Cauchy may be most advantageously employed ; and had 
he pursued his researches in this direction, his labours would doubtless 
have been attended with more success, and with greater benefit to 
science. SS 
LONDON ELECTRICAL SOCIETY. 
[Continued from p. 232.] 
Feb. 18, 1843. (Meeting for illustration.)—A Lecture was de- 
livered before the Society, by Mr. Henry Letheby, M.B., A.L.S, &c., 
“On Animal Electricity,” in illustration of the reasons advanced 
in a paper read at a recent meeting in favour of the theory which 
