M. MELLONI ON THE POLARIZATION OF HEAT. 339 
Tas_e III. 
Source of heat, the flame of a Locatelli lamp. 
3 lek 
5 Calorific transmissions s q = = 
NAMES 5: 3 through each interposed layer and |5 5 ne 
oS * the same pair of tourmalines Eeo5 
of the = 3 - (No. 5 in the first table) See B 
substances interposed 2 g g in the position of the axes. ero eS @ 
before the introduction |< 2 2 5 2 aS 
épthe 623) ee 
calorific radiation r= g 5 Parallel. Perpendicular. = = e g i 
into the 3 enn we R.2 a i i) 
tourmalines. = = a ag bed eT i cee fF 
I ofimpul-| Forces. |ofimpul-| Forces. 8 2 = 3 a 
Ss sion. sion. = S53 
mm cs) o 
PUPECRCETI Go cicceccvencsns 0:00 | 17°11 | 14°84] 15°15) 13°15) 11°35 
Glass blueish green ...| 1-93 | 17°65| 15°30} 15°54| 13°49} 11-83 
opake black ...... 1:98 | 17:10] 14°83] 15°06] 13:05} 11-94 
Sulphate of Barytes ...| 2-60 | 17°33 | 15°03} 15°23 | 13°21} 19-07 
ei) ) 00/2 8°49 | 17°52} 15°19} 12°95} 19°80} 15°65 
Sulphate of Lime ...... 2°71 | 17°76 | 15°39 | 12°74) 12°63} 17°91 
Glass uncoloured ...... 1°85 | 17:27} 15°08} 16°24] 14°11 646 
MDTEO US be. sohiad.k 8:27 | 17°81 | 15°43} 17:05.) 14°79 4°17 
Glass coloured (red) ...| 1°80 | 17°49} 15°16} 16°32| 14°17 6°53 
— (orange)} 1°87 | 16°91) 14°67| 15°77| 13°69 6°70 
——_——_——-(yellow)} 1°79 | 17-22} 14°93} 16°12] 14-00 6°15 
—_—- blue)... 1°83 | 16°87} 14°64} 15°81 | 13°73 6°20 
indigo)| 1°78 | 16°98} 14°73 | 15°86 | 13°78 6°44 
violet)..| 1°81 | 17°30) 15:00] 16°20} 14°06 6°29 
It is to be observed that the extreme limits of the variations produced 
in the index by the interposition of the screens differ considerably less 
than they did: relatively to the pale yellow tourmalines ; a circumstance 
which indicates a greater homogeneity in the calorific stream trans- 
mitted by the tourmalines actually employed. Moreover, the index of 
polarization undergoes but a very slight alteration under the influence 
of the green and the opake-black glasses, which produced a reduction 
of between twelve and nineteen twentieths in the direct index of the 
table that precedes the above. The diathermancy of these green tour- 
malines is therefore analogous to that of the green and the opake-black 
glasses. 
As to the white, red, orange, yellow, blue, indigo, and violet glasses, 
they diminish the index of polarization instead of leaving it in its natu- 
ral state, as in the instance of the pale yellow tourmalines. In this 
there is nothing that should surprise us, since the difference of diather- 
mancy proper to the two polarizing systems causes these uncoloured and 
