42 . Ms MELLONI ON THE IMMEDIATE TRANSMISSION 
being, in those different circumstances, submitted to the same quantity 
of radiant heat, the different degrees of diminution suffered by this heat 
in passing through it must evidently be attributed only to the peculiar 
quality of each radiation. This reflection will give still greater force 
to the truth of the consequences which we are about to deduce from the 
results of our experiments, 
Seven plates of glass of different degrees of thickness submitted to 
the action of the fou sorts of calorific rays in succession have given the 
following transmissions : 
Transmissions of the glass out of 100 rays 
‘ of heat issuing from 
Thickness |—___. 
eesky nee ———_-+———_-+, 
of the blackened | blackened 
plates. a Locatelli | incandescent copper copper 
lamp. platina. {heated to a30° heated to 100° 
Ws 57 
54: 37 
46 31 
41 25 
37 20 
585 18 
33°5 17 
o™™- 07 
an 
ODPNr oS 
Although we do not exactly know the degree of heat given by the 
flame of oil or by platina kept in a state of incandescence by an alcohol 
lamp, we are nevertheless quite certain that the first of these possesses 
a higher temperature than the second, and that this again exceeds the 
390° of the first plate of copper. Now a glance at the table is sufficient 
to show that the number of rays transmitted by the same plate decreases 
with the temperature of the calorific source, a fact which confirms the 
well-known law of Delaroche. But the decrease is more or less rapid 
in proportion to the greater or less thickness of the plate. 
Let OM, ON, (Plate I. Fig. 1.) be two rectangular axes of the same 
length; let the first represent the thickness of the screen of 8™™ and the 
second the total quantity of incident heat. Let us mee OM into stapes 
Oa, O04, re Od, Oc, 4 respectively equal to ° “OM, 570M, = 3 OM, 
a OM, z OM, and OM; and. : ease the pin of aeeen let us _ 
draw a sciipeneibalas éa'= pL ON, b' =F, ON, ccd = Fo ON, 
dd’ =# ON, ed =, ON, ff! = BON, Mg' = 3 ON. Thecurve 
(ab! c' d' e' f'g') passing through the extremities of these perpendicu- 
lars will represent the decreasing intensity of the Locatelli lamp at each 
point of the screen of 8™™ in thickness. 
7 
