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 witli 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 i-ays 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, thefiame of a Locatelli lamp. 



Colour 



of 



each pair 



of 



tourmalines. 



Deep green 30-56 



Bluish green 29*81 



Blue green 32-35 



Yellowish green 31 -42 



Yellowish green 33-23 



Yellow green 31-96 



Reddish brown 29*89 



Muddy violet 30-69 



Pale j-ellow 31-27 



Calorific transmissions 

 in the position of the axes. 



Parallel. 



Arcs 

 of impul- 

 sion. 



Forces. 



27-50 

 26*51 

 29*40 

 28*51 

 30*18 

 29*07 

 26*62 

 27*67 

 28*37 



Perpendicular. 



Arcs 



ofimpul- 



sion. 



Forces. 



29*78 

 28*22 

 30*11 

 29*32 

 30*01 

 29*11 

 25*32 

 25*45 

 25*60 



26*48 

 24*60 

 26*90 

 25*89 

 26*77 

 25*61 

 21*88 

 22*00 

 22-16 



■C -73 o J= 



3-71 



7*20 



8*50 



9*19 



11*30 



11*90 



17*72 



20*48 



21*89 



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 " arcs 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 arc described in consequence of the transmission through the plates 

 with their axes parallel was first observed, and then the arc described 

 in consequence of the transmission through the same tourmalines with 



