294 
SECOND REPORT - 1832 . 
4thly, It has been found by experiment, that with prisms of 
crown glass the maximum heating effect is in the middle of the 
red space. Unfortunately the relation between the maximum 
heat in the water spectrum and in the crown glass spectrum 
has not been ascertained. If we suppose them equal, it appears 
that the crown glass must have exercised a greater absorptive 
action than the water upon the more refrangible rays , and a 
less absorptive action upon the less refrangible rays ; in the 
same manner as is done by red glasses upon light, 
A prism of sulphuric acid gives the maximum ordinate of 
heat in the orange space ; or the fluid absorbs more of the red 
rays than crown glass, and less of the rays on the other side of 
the orange. 
In flint glass, where the maximum heat is at the very extre¬ 
mity of the spectrum, scarcely any of the red rays are absorbed, 
while great proportions of ail the others are. 
Dr. Turner \Chem. p. 84, 3rd edit.) says, that it is difficult 
to account for Seebeck’s results without supposing that differ¬ 
ent media differ in their power of refracting caloric {i. e. the 
heating rays of the sun.) 
Sir D. Brewster considers that the true explanation is that 
which the above principles afford, viz. that colourless transpa¬ 
rent bodies, in acting upon the solar heat, exercise the same 
sort of absorptive action upon it, that coloured transparent 
bodies do upon light; the maximum ordinate shifting its posi¬ 
tion with the nature of the body. Coloured media give some¬ 
times two or more maxima of light, with large spaces and small 
lines entirely defective of light, in consequence of the absorp¬ 
tion being total at those places. 
In like manner he is persuaded it will be found that there 
are defective spaces and lines in the spectrum of solar heat; 
these he thinks may possibly be detected by using as thermo¬ 
meters the minute natural cavities in topaz, &c., filled with 
fluid or vapour, and not more than 0*001 inch in magnitude. 
5thly, These views are exactly accordant with the results of 
Sir W. Herschel above stated. 
They are equally consistent with the facts, whether the curve 
of heat terminate abruptly at the extremity of the red space, 
or continue beyond the visible spectrum. 
Sir D. Brewster has by particular methods of condensation 
succeeded in detecting- both heat and light at considerable di- 
stances beyond the maximum of heat, with a flint glass prism ; 
that is, rays undergoing very little refraction. 
He considers it highly probable that the deoxidizing rays 
will be found to be subject to the same laws of absorption as 
