M. MELLONI ON THE POLARIZATION OF HEAT. 333 
One of the plates is fixed, the other is moveable together with that half 
of the box in which it is contained. Marks traced on their edges enable 
us to distinguish with ease the two principal positions of the axes of 
crystallization. 
I exhibit here in a single table the results which I obtained by ope- 
rating on nine pairs of tourmalines borrowed from different individuals. 
All these pairs polarized luminous rays almost completely ; that is to say, 
that to a person looking at the flame of a wax taper through each of 
these systems, it appeared sufficiently vivid and brilliant, so long as the 
axes were parallel; but the image became nearly extinct when the axes 
were perpendicular. 
TABLE I. 
Source of Heat, the flame of a Locatelli lamp. 
Calorific transmissions 
in the position of the axes. 
Colour 
of aE RTS TARE F cureiey 
each pair Parallel. Perpendicular. 
of 
poe |) ees 
tourmalines. 
Arcs Arcs 
ofimpul-| Forces. |ofimpul-| Forces. 
sion. sion. 
——— — — — _—————_ 
Indices of polarization in 
the axes are parallel. 
Numbers indicating the order. 
hundredth parts of the quan- 
tity of heat transmitted when 
Deep green 30°56 | 27°50 | 29°78'| 26°48 
Bluish green 29°81 | 26°51 | 28°22 | 24°60 
Blue green 32°35 | 29°40 | 30°11 | 26°90 
Yellowish green 31°42 | 28°51 | 29°32 | 25°89 
Yellowish green 33°23 | 30°18 | 30°01 | 26°77 
Yellow green 31°96 | 29:07 | 29°11 | 25°61 
Reddish brown 29°89 | 26°62 | 25°32 | 21°88 
Muddy violet............| 30°69 | 27°67 | 25°45 | 22°00 
Pale yellow...............| 31°27 | 28°37 | 25°60} 22°16 
OO~TD HP OOM eH 
After what we have already stated, the numbers in the four columns 
which: precede the last require no explanation. I have therefore only 
to observe, that each number under the head “ares of impulsion” re- 
presents the mean of several observations, made alternately in the paral- 
lel and in the perpendicular positions of the axes; that is to say, that 
the are described in consequence of the transmission through the plates 
with their axes parallel was first observed, and then the are described 
in consequence of the transmission through the same tourmalines with 
