193 
The following letter from Sir John F. W. Herschel, Bart., 
M.A., F.R.S., &c., dated Collingwood, April 28th, 1868, was 
read : — 
I am so accustomed to see passages from my own writings 
cited in direct opposition to their literal meaning and in 
support of views directly adverse to those entertained by 
myself, and which they were written to explain or to advo- 
cate, that I should hardly have thought it worth while to 
notice one more instance of the kind in the paper read at 
the meeting of the Phil, and Lit. Society on the 14th inst. 
by Mr. J. C. Dyer, but for a general impression of the inex- 
pediency of silence on such occasions. I allude to his state- 
ment that in treating of the undulations of light I have 
somewhere or other estimated and given in figures the 
amount of “ resistance to the transit of light through space” 
of what he terms the “ luminous ether,” (the double commas 
in this last case being his own) — meaning, I suppose, the 
luminiferous ether — a distinction ever by myself most care- 
fully attended to. This is very much as if one should speak 
of the resistance of air to the propagation of sound — of steam 
power to the conveyance of information by mail-train or of 
electricity to its conveyance by telegraph — or of the resist- 
ance of gunpowder to the propulsion of a cannon ball. It 
is true that in the article cited I have endeavoured to esti- 
mate and to state in figures the intensity of the elastic forces 
effective in the propagation of light— but assuredly I never 
expected to see this construed (if that be the estimate 
referred to) into the exact opposite of what it obviously 
means. 
If, on the other hand, Mr. Dyer should have had in view 
any passage in any other of my writings in which I may 
have spoken of the doctrine of the imperfect transparency 
of the celestial spaces, propounded (if I mistake not) by 
Olbers ; I may be allowed to explain once for all, that I 
never advocated that doctrine and do not believe in it. 
