REPORT ON RADIANT HEAT. 38 
the observations accord much better with the law of Fresnel 
than with that deduced by Mr. Potter. In the instance of me- 
tals, Prof. Forbes considers Mr. Potter’s discovery verified, that 
the reflexion is less intense at higher angles of incidence : he has 
not yet been able to verify Prof. Maccullagh’s ference, that it 
has a minimum before reaching 90°; and lastly, he observes that 
the quantity of heat reflected from metals is so much greater 
than Mr. Potter’s estimate for light, as to lead him to suspect 
that all that gentleman’s photometric ratios are too small; this 
would nearly account for their deviations from Fresnel’s law. 
He has also made some attempts for verifying that law by ob~ 
servations on heat polarized in opposite planes. 
Mr. Potter, it is well known, mainly founds his objections to 
the undulatory theory on the discrepancy between Fresnel’s law 
for the intensities of reflected light and his own photometrical 
determinations. He has therefore naturally been led into some 
controversial remarks on Prof. Forbes’s results in a paper in the 
London and Edinburgh Journal of Science, to which Prof. 
Forbes has replied. 
Considering that the whole inquiry is as yet confessedly in 
an incomplete state, any further observations upon it in this 
place would be premature. 
Conclusion. 
In thus reviewing the different points of inquiry which have 
been of late pursued relative to radiant heat, and the several 
important discoveries with which that research has been re- 
warded, I have for the most part preserved, under each head, the 
chronological order. 
The progress of discovery is here, I trust, too clearly marked 
to allow any real ground for these questions as to priority and 
originality, which have given rise to so much unhappy contro- 
versy between rival philosophers; or to the less open, but 
equally lamentable manifestations of jealousy, in ambiguous ex- 
pressions of claims, into which men of science have been some- 
times betrayed. The dispassionate reviewer of the history of dis- 
covery at once best avoids all such controversial topics, and ful- 
fils the demands of critical justice, by a simple but careful 
statement of facts. 
In the present instance it appears to me that the share of cre- 
dit due to the distinguished parties respectively, who have co- 
operated to introduce the discoveries above reported, is sufli- 
ciently well-marked, and certainly ample enough in each in- 
stance to confer the highest celebrity on those who have borne 
the chief portion of the labour. 
VOL, 1x. 1840. D 
