324 Intelligence and Miscellaneous Articles. 



For distance of a metre this would give about 160,000 volts total 

 difference of potential. — Wiener Berichte, Feb. 9, 1888. 



INFLUENCE OF LIGHT ON THE THERMAL CONDUCTIVITY OF CRY- 

 STALLIZED SELENIUM. BY MM. BELLATI AND E. LUSANA. 



The authors investigated whether light has any effect on the 

 conductivity for heat of crystallized selenium, and have found 

 that such an action does exist. Circular laminae of crystallized 

 selenium were prepared of about 0*03 to O'0-l cm. in thickness, 

 and about 2*5 cm. diameter, and were coated over with a thin layer 

 of the double salt Cal 2 , Hgl 2 . At ordinary temperatures this double 

 salt has a bright red colour, but when heated to 70° it becomes of 

 a dark chocolate- brown. One point of the selenium-plate was then 

 heated by pressing against it the apex of a V-shaped platinum- 

 wire, which was traversed by an electrical current. When thermal 

 equilibrium was established, the chocolate-brown colour had ex- 

 tended to a circle of a definite diameter. The experiment was 

 frequently repeated, partly when the selenium-plate was kept dark 

 and partly when it was under the influence of light. The source 

 was sunlight, which had passed through ammoniacal sulphate of 

 copper in order to eliminate the heat-rays. In each case the 

 diameter of that circle was determined to which the change of 

 colour had extended. The following table may serve as an ex- 

 ample, in which D denotes the diameter measured according to a 

 definite unit ; — 



Without light. 



D. 116 

 116 

 11.5 



Mean . . 115 - 7 Mean 



Hence we have for the ratio of the thermal conductivities, with 

 and without illumination of the areas, 1-13. Light accordingly very 

 appreciably favours conductivity in selenium. The authors show, 

 in conclusion, that the change of electrical as well as of thermal 

 conductivity in consequence of the action of light is of the same 

 order of magnitude. — Beiblatter der PhysiJc, vol. xi. p. 818 (from Atti 

 del R. 1st. Ven. vol. v. 1887). 



