M. MELLONI ON THE POLARIZATION OF HEAT. 84] 
malines enables us to advance a step further; for this equality shows 
that not only the quantity but the quality of the heat transmitted by 
pure water is the same as the quality of that transmitted by water 
saturated with salt or alum. In short, if we receive on the pile the 
ealorific streams which issue from distilled water, and the solutions of 
rock salt and alum, we shall find the deviations in the galvanometer 
very nearly equal in the three cases. It is to be recollected, however, 
that this will happen only when the three layers from which the rays 
issue are of the same thickness. Now this invariability of action through 
layers of equal thickness takes place also if we interpose the same plate 
of alum or any other substance behind each of the liquid layers in suc- 
cession ; for the common deviation is always diminished by a constant 
quantity, even when, by concentrating the calorific radiation with lenses, 
we have raised to 35° or 40° the are of impulsion described solely under 
the action of the stream transmitted by each of the liquid layers. 
In order to conclude the experimental study of the calorific polariza- 
tion of the tourmalines, we have only to compare with one another the 
polarizing action of these crystallized substances on the radiations of 
different sources of heat. For this purpose I select the four systems 
marked Nos. 1, 5, 8, and 9 in the first table, and these being exposed, 
in the two principal directions of the axes, to the calorific radiations of 
an Argand lamp, a Locatelli lamp, a spiral of incandescent platina, and 
a plate of copper heated to 400°, give the indices of polarization con- 
tained in the following table. 
Taste IV. 
= 
o 
= £ Indices of polarization for the direct 
o = radiations 
ES Colour oe 
8 of ie z sain 
= ‘3 each pair f of the 
SES! Ke o platina kept] of a plate 
aed e 5‘ the Argand} of the in a state | of copper 
25 tourmalines. lamp with /[, ocatelli | of incan- | heated 
gs a glass lamp. descence | te about 
Bs funnel. by the flame} 400°C. 
Z, of alcohol. 
Deep green ......... 0°37 S71 5°27 0°59 
Yellowish green...... 5°33 11°30 13°89 3°22 
Muddy violet ........) 24-50 90°48 17°20 9-30 
Pale yellow .......,.| 26°21 91°89 18°16 9-98 
OoOne 
N.B. In this table the ares of impulsion are omitted in order to avoid exces- 
sive complexity. We think it necessary, however, to observe that these were 
often more extensive than those of the preceding tables; and this was indeed 
absolutely necessary in order to perceive those indices which in many instances 
are extremely feeble. No.1, for example, being exposed to the radiation of the 
Vor. l—Parrt II. DA 
