Intelligence and Miscellaneous Articles. 477 



bounding surface of glass than would a concave surface. In this 

 way the behaviour of the cup-shaped radiometer with both surfaces 

 bright, No. 1035, can be understood, and perhaps also that of Nos. 

 1038 and 1039. It would not be difficult to test this view experi- 

 mentally, by placing a small mica screen in the focus of a concave 

 cup, where the molecular force should be concentrated. But it is 

 not easy to see how such an hypothesis can explain the behaviour 

 of No. 1037, where the action of the bright convex surface more 

 than overcomes the superior absorptive and radiating power of 

 the concave black surface ; and the explanation entirely fails to 

 account for the powerful attraction which a lighted candle is seen 

 to exert on the concave surfaces in Nos. 1035, 1037, and 1039. 



LXIV. Intelligence and Miscellaneous Articles. 



RESEARCHES ON THE METALLIC REFLECTION OF POLARIZED 

 OBSCURE HEAT-RAYS. BY M. MOUTON. 



I HA YE employed, in these researches, one of the apparatus ordi- 

 narily used by M. Desains for studying heat-spectra. Polarized 

 in a determinate azimuth, the light and heat traversed first a plate of 

 flint glass suitably inclined to the plane of incidence, and intended to 

 nnul the effects produced by the prism *. The pencil, reflected, 

 then dispersed and analyzed, was finally resolved into a very pure 

 spectrum, the luminous portion of which was directed to the slit of 

 the thermoelectric pile. The breadth of this slit was 1 millim. ; 

 that of the red band of the luminous spectrum 4 millims., and the 

 total extent of the luminous spectrum about 4 centims. 



I operated on three wave-lengths (\ v X. 2 , X 3 ) distributed in the 

 obscure portion of the spectrum, and sensibly symmetric in refer- 

 ence to the extreme red : — A 1? of the yellow ; X 2 , of the blue-green ; 

 and X 3 , of the indigo. The method of experiment rests on princi- 

 ples established by M. Jamin in his " Etudes de la reflexion metal- 

 lique de la lumiere"t: — 



1. Every ray initially polarized in any other azimuth than zero 

 and 90° becomes, after reflection, elliptic. 



2. After passing through a spar prism, of which only the extra- 

 ordinary image is utilized, an elliptic ray presents, when the prin- 

 cipal section of the prism coincides with the major axis of the 

 ellipse, a maximum of intensity — with the minor axis, a minimum; 

 and if we study these intensities in pairs of azimuths a and a + 90°, 

 going from the major to the minor axis, the first predominates over 

 the second as long as a is comprised between the major axis and 

 45°, becoming inferior to it as soon as a passes beyond that bisec- 

 trix of the axes. Thus the source of heat is only required to be 

 constant during each pair of observations, a period which is ren- 

 dered very brief by a special movement permitting the analyzer to 

 be rotated rapidly through 90°. The azimuth of the bisectrices of 

 of the axes of the ellipse can thus be determined within 1 degree. 



* Fizeau and Foucault, Ann. de Chim. et de Phys. 3 e serie, t. xxx. p. 147. 

 t Ibid. t. xix. p. 321 seqq. 



