148 



Intelligence and Miscellaneous Articles. 





K 



A 

 A ' 



Brightness. 

 K. 



1. Swan lamp \ 



I 



2. Edison lamp ... J 



3. Bernstein lamp . . 1 



4-895 10 8 

 6-719 10 8 

 7-523 10 8 

 8-560 10* 



5-818 10 8 



7-409 10 8 



9259 10 8 



11-208 10 8 



12-289 10 8 

 16-163 10 8 



18-895 10 8 

 23 905 10 8 



0-023 

 0028 

 0-036 

 0-052 



0036 

 0042 

 0-062 

 0085 



0042 

 0-065 

 0073 

 0-099 



2-62 



9 24 



13-24 



20-60 



401 



8-29 

 16-98 

 28-65 



The values deduced from the experiments show that incandescent 

 lamps exhibit somewhat different deportment as regards con- 

 ductivity. While the Swan lamp with a brightness of 20 candles 

 gives an optical useful effect of 5 per cent., Edison and Bernstein 

 lamps give for the same luminosity an effect of 7 per cent. 



The optical useful effect of all the lamps increases with the 

 temperature. With the highest temperature of incandescence, 

 this can be raised to 10 per cent. With the normal temperature 

 of ignition, when the luminosity is that near 16 candles, it does 

 not exceed 5 to 6 per cent. ; that is, of the total electrical energy 

 used for -working the incandescent lamp only 5 to 6 per cent, is 

 available for illumination. The rest in the form of obscure 

 radiation, amounting to 94-95 per cent., is lost as far as light is 

 concerned. — Inaugural Dissertation, Zurich ; Beiblatter der Physik, 

 No. 11, 1890. 



ON THE CONDUCTIVITY OF SNOW. BY S. A. HJELTSTROM. 



From the great importance in nature of the thermal deportment 

 of the snow layer, the author made experiments on the daily 

 variations of the temperature at different depths in the snow, in 

 order to calculate therefrom the thermal conductivity of snow. 

 The bulb3 of the thermometers were at a depth of 1, 11, 21, and 

 31 centim. below the surface of the snow. The snow near the 

 thermometers was protected against the direct rays of the sun by 

 a bank of snow on the south. The weather unfortunately did not 

 allow of series of observations being carried on for a long time. 



Taking the specific heat of snow as equal to that of ice, 0*50, and 

 for its density the value determined on the spot by the author, 

 0*183, the absolute conducting-power may be determined from 

 Angstrom's formula to be 



0-0269, 0-0343, 0-0302, Mean 0-0304, 

 the units being C.Gr.S. The conductivity of snow is accordingly 

 about one seventh that of moist clay (0-226). — (Efvers. Act. Stock- 

 holm, xlvi. p. 669 (1889); Beiblatter der Physik, vol. xiv. p. 1196. 



