Mr. Potter on Photometry hi connexion with Physical Optics. 1 7 
It is thus that almost any analysis, which professed to sup- 
port the undulatory theory of light, has been hailed as a mag- 
nificent achievement without its minute bearings being ever 
looked into, provided the general case showed eiprimd facie 
accordance with some known facts. In no place has this been 
more prominent than in the Cambridge Philosophical Society. 
He is a young man and inexperienced who has so little 
knowledge of human nature as to suppose that in this state of 
matters any scientific truth, of however important a bearing, 
which did not fall in with the popular and fashionable prepos- 
sessions, must be decried, and its discoverer would naturally 
be held out as a factious and refractory pretender in the re- 
public of science. 
The scientific public must sooner or later awaken and per- 
ceive the liberty which has been taken with its confidence, 
and there must sooner or later arise a time of return to sound 
philosophizing in physical optics, when the maxims of Lord 
Bacon will be acknowledged as the only sure guide. 
My objections to Fresnel’s formulae for the intensity of light 
reflected and transmitted by transparent bodies, although 
founded on laborious and careful experimental reseaixhes, 
have been treated as though other men’s guesses were more 
worth than my experiments. I shall, however, before I close 
this paper, bring corroborative evidence of the accuracy of 
my results which fortunately exists in print amongst the la- 
bours of Bouguer and of Sir William Herschel. Dr. Faraday 
also has given some photometric measures in his Bakerian lec- 
ture on the manufacture of glass for optical purposes. If the 
refractive indices of the heavy optical glass had been given, we 
should have had a good test of Fresnel’s formulae from the 
experiments with those glasses. The angle of incidence which 
Dr. Faraday employed does not furnish an experimentum crucis 
for common glass. 
The subject of photometry has been discussed by Professor 
Lloyd in his report on Physical Optics, read before the 
‘ British Association for the Advancement of Science;’ by 
Professor Powell, in a paper read before the Newcastle meet- 
ing of the Association, and lately, by Professor Forbes, in a 
paper read before the Royal Society of Edinburgh, of which 
an abstract has been printed under the title “ Memorandum 
on the Intensity of reflected Light and Heat. By Professor 
Forbes. (From the Proceedings of the Royal Society of 
Edinburgh, March 18, 1839).”^' 
As Professors Lloyd and Powell did not think it necessary 
to make, themselves acquainted v/ith the subject they under- 
[* Inserted in L. and E. Phil. Mag. for December 1839, vol. xv. p. 479.] 
Phil. Mag. S. 3. Vol. 16. No. 100. Jan. 1840. C 
