64 M. MELLONI ON THE IMMEDIATE TRANSMISSION 
manous substances examined by that process to which we have sub- 
mitted the coloured glasses and the diaphanous colourless bodies. 
Screens emitting 100 rays of heat which 
are made to fall successively on 
the same slice of alum. 
Number of rays 
transmitted by this slice. 
Mica, black: opake 20.0.5. scosccsstene cus 2 
Tourmaline, -greenccccescesveovewe teases OFT 
Sulphate of barytes ..........sseeeeeeeee 12 
Acid chromate of potash ............. 14 
IMI1G as <WIRILE: rasetcteeccerecergere slestardetelennce Mee 15 
Beryl cscs. tvs veeivscwseneboethdshatected, Le 
Emerald ogy siceceie St sedeesecveed eanseeeted LO 
Agate, pearly.........sceceeceeeeeeeeeeeees 24: 
Agate, yellow ....ccscccccccecsevseeeceveee 24 
Amber, yellow .......0s0ecesesesereeeeee 3O 
GOI. oie ree aa'snie wna tween jen tee seensecertes 45 
On these numbers we have two remarks to make: first, that the green 
tourmaline and the black mica act in a manner analogous to glass of 
the same colour; second, that the beryl and emerald emit rays equally 
transmissible by the alum, although the colours of these two kinds of 
the same substance are different. The same happens to the two kinds 
of agate. These facts may perhaps be turned to some account by the 
mineralogist in examining certain coloured substances which belong to 
the different varieties of one mineralogical species. 
We have been hitherto investigating the action of alum on a constant 
quantity of rays emerging from several diathermanoys substances. Let 
us now reverse the problem and see what will be the effect when these 
substances are interposed in the passage of an invariable radiation is- 
suing from alum. 
In the third column of the following table will be found the results 
furnished by this class of experiments. It is almost unnecessary to ob- 
serve that they have been obtained by successively placing the several 
bodies between the alum and the pile, after having produced in the 
galvanometer the ordinary deviation of 30° through the first substance. 
I have placed in the columns after the third the values of the trans- 
missions of the same bodies exposed to the rays emerging from four 
substances different from alum; namely, sulphate of lime, acid chromate 
of potash, and green and black glass. The natural values of the calorific 
transmissions, that is to say, the results obtained under the immediate 
action of the lamp, are indicated in the second column. 
