316 Proceedings of the British Association. 
_. The report then went on to the researches of Melloni on the 
reflection of heat ; and the analogies a and heat, as traced 
by Forbes and Melloni. He dissents from the opinion of Am- 
pere, that the difference between heat and light is to be aecou ed 
for by the difference of wave length on the undulatory hypoth- ~ 
esis. During these researches, he found that a certain kind of 
green glass colored by oxide of copper, though it permitted a por- 
tion of luminous rays to pass, absorbed all the calorific rays, so 
that it exhibited no calorific action capable of being rendered per- 
ceptible by the most delicate thermoscope, even when so concen- 
> 1h" oo 
trated by lenses, as to rival the direct rays of the sun in brilliancy. 
‘ With respect to the transmission of heat by screens, Prof. F’. re- 
marked that Melloni’s view of the transmission of heat of low 
temperature, by all substances alike, is equivalent to saying that 
substances in general allow only the more refrangible rays to 
pass, or that while rock-salt presents the analogy of white glass, 
by transmitting all rays in equal proportions, every substance 
hitherto examined acted on the calorific rays as. violet or blue 
glass does on light, absorbing the rays of least refrangibility, and 
transmitting the others only. To this rule, Melloni made out 
the first exception, or the first analogue to red glass,—trock-salt 
with its surface smoked. Prof. F. soon pointed out another, via. 
mica split by heat into numerous fine lamine, and hence, as the 
effect was obviously mechanical, (since unlaminated mica pro- 
duces no such effect,) he concludes that the smoked surface of 
the rock-salt acted also mechanically, and was thus led to try the 
effects of surfaces variously altered by mechanical means; and 
thus effects in some distant degree analogous to sifting the heat, 
were observed. Fine powders, also sifted on the surface, were 
found to affect the transmission of heat, and these Prof. F. con 
sidered analogous to diffraction and periodic colors in light. From 
these important researches, we have learned to connect modifica- 
tions in the transmission of heat with the quality of refrangibility, 
and not as heretofore with a supposed difference of quality ae 
pending on the source of the heat. ‘The report then gave an a6 
count of the researches of Dr. Hudson on radiation of heat, those 
of President Bache and Stark on the influence of color and ced 
face on radiation, and Prof. P.’s experiments upon the repulsive 
power of heat; and adverted to Mr. Farquharson’s theory of the 
formation of ice at the bottom of rivers, as a result from radiant 
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