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 1 00 rays of heat which ^^^^^^^^, ^^ 



are made to fall successively on transmitted by this slice, 



the same slice ot alum. •' 



Mica, black opake 2 



Tourmaline, green 7 



Sulphate of barytes 12 



Acid chromate of potash 14 ' 



Mica, white 15 



Beryl 19 



Emerald 19 



Agate, pearly 24 



Agate, yellow 24 



Amber, yellow 30 



Gum 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 diathernianovjs substances. Let 

 us now reverse the problem and see what will be the effect when these 

 substances are interposed in the passage of an iuA-ariable 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. 



