M. MELLONI ON THE POLARIZATION OF IIKAT. 337 



We have found by transmission that the rays emerging from the green 

 and opake-black glasses may be said to possess properties diametrically 

 opposite to those of the rays issuing from alum*. The same antagonism 

 of properties is manifested with respect to the apparent polarization 

 which these two species of heat undergo in their passage through the 

 tourmalines ; for in the one the index of polarization increases three- or 

 four-fold, while in the other it suffers a diminution of eight or nine 

 tenths. 



In fine, experiment has shown that the calorific rays immediately trans- 

 mitted by alum approximate closely to the luminous rays, both in their 

 abundant transmission through all uncoloured diaphanous substances 



form of the calorific spectrum preserved with great regularity, as we have seen 

 elsewhere {Ann. de Chim. et de Phys., torn. Ix. p. 426. ; Scientific Memoirs, vol. i. 

 part i.), thai is to say, possessing one maximum, and lower temperatures regu- 

 larly decreasing on each side of it, but we see that the distances from this maxi- 

 mum andthe surrounding bands toagiven zone of theluminous normal spectrum 

 remain sensibly invariable. As to the absolute quantity of heat, it varies con- 

 siderably with the tint and nature of the glass ; but this variation is always 

 jiroportional to the value of the ordinates which represent the temperatures of 

 the different zones for any one of the coloured plates ; so that the intensities of 

 the maxinmm and the adjacent bands are more or less affected in a constant 

 ratio through the whole extent of each new spectrum produced by changing 

 the glass. From these two facts it clearly follows that the quality of the calo- 

 rific stream transmitted by the different plates of coloured glass does not vary 

 in its passage from one plate to another. In this however, as in the other ana- 

 lyses that we have made of this phfenomenon, the green glass possessing the 

 qualities already mentioned presents a ver}- striking exception : for this species 

 of glass displaces the calorific spectrum and throws it, in the direction of the in- 

 ferior refraction, almost totally beyond those limits that are common to the 

 spectra produced by all the other species of coloured glass. 



WI.en several different methods (and the processes of absorption, polarization, 

 and refraction described here and elsewhere are really such,) lead to one and the 

 same conclusion, it seems to me that the conclusion is sufficiently secure to be 

 ranked among truths firmly established by experiment. 



Thus the colouring matters of the coloured glasses, while they so power- 

 fully affect the relations of quantity which the different rays of ordinary light 

 bear to each other, exercise no elective action on the concomitant calorific 

 rays. This curious phoenomenon is the more remarkable, as the same colouring 

 matters absorb, almost always, a very considerable portion of the heat naturally 

 transmitted by tlie glass. The following are, in fact, the calorific transmissions 

 of the seven coloured glasses referred to the transmission of the colourless glass 

 which is repi-esented by 100 : Red glass 82'5, Orange 72-5, Yellow 55, Bluish 

 green 57'5, IJlue 52'5, Indigo 30, Violet 85. The quantity of heat absorbed 

 through the action of the colouring substances is therefore 17'5 in the red glass, 

 27'5 in the orange, 45 in the yellow, 42-5 in the green, 47'5 in the blue, 70 in 

 the indigo, and 15 in the violet. Now, as these absorptions extinguish a pro- 

 portional part of each of the rays which constitute the calorific stream trans- 

 mitted by common glass, they may be compared, as we said before, with the 

 al)sorbent action exercised on light by matters more or less deeply brown or 

 dark when they are immersed in water or some other colourless liquid which 

 dissolves but does not affect them chemically. 



• Ann. de Chim. et de Phys., torn. Iv. p. 382. 



