6 REPORT—1840. 
With this view (following a similar mode of operation to that 
adopted in the last instance) he used successively glasses of 
different colours, for each of which the distance of the source 
was varied till a standard effect (about 40° deviation of the 
needle) was produced on the galvanometer. In this position, in 
each case, a plate of sulphate of lime was then interposed, and 
diminished the deviation to about 18° for all the coloured glasses 
except green, in which case it was to about 8°. When alum 
was substituted the deviations were reduced in the first case to 
8°, in the second to 1°°6. Hence he concludes that all the co- 
loured glasses, except green, produce no “‘ elective action”’ on 
heat; green glass, on the contrary, transmits rays more easily 
stopped than the others. 
Connecting this with his other inference, that rays are 
stopped in proportion to their refrangibility, he instituted 
another series of experiments to put this to the test. The 
sources of heat compared were an argand lamp and incandescent 
platinum, the rays of heat from the former being the more 
refrangible. The quantities of heat from the lamp and the 
metal transmitted by the green glass were nearly equal; by all 
the others, nearly in the ratio of 2 to 1. Hence he infers that 
green glass is more diathermanous for rays of less refrangibility. 
Again, the rays transmitted by citric acid and some other 
substances, are those only of the greatest refrangibility. They 
should, therefore, be the least transmissible by green glass. 
This was found to be the case. Of 100 rays passed through 
citric acid, all the other glasses transmitted various preparations, 
from 89 to 28, while green glass transmitted only from 6 to 2. 
Without the citric acid, the rays from incandescent platinum 
were more copiously transmitted by the green glass than by the 
others. 
The whole of the rays of low refrangibility emitted by the 
platinum, and for which alone the green glass is transparent, 
had been stopped by the interposition of the plate of citric 
acid, which had, as it were, sifted it free from these rays. 
Hence the author concludes, that “ green glass is the only 
kind which possesses a COLOURATION for heat (if we may use 
the expression), the others acting upon it only as more or less 
transparent glass of uniform tint does upon light.” 
In a subsequent part of the memoir, M. Melloni gives a 
tabular view of the effects observed in the same manner, of the 
constant radiations emitted from six different substances, each 
intercepted successively by 24 minerals and 10 coloured 
glasses ; from which it appears that the transmission is very 
different, according to the nature of the first medium. 
