isparency of flame. From one 1 

 lighthouse lamps, having a diameter of from 



146 Scientific TntelUgence. 



9. Transparency of Flame and of the ^Im— M. E. Allakd has 

 presented to the French Academy several memoirs on the absorp- 

 tion of the light of lighthouse^ lamps. The first r • ^ • - 



raps, 

 nparison of the luminous intensity of the flames shows 

 that the brightness increases a little less rapidly than the con- 

 sumption of the oil ; comparing the intensity with the dimensions 

 of the flame, it appears that the brightness per square centimeter 

 increases, but that per cubic centimeter diminishes with the size 

 of the flame. This difference may be accounted for by assuming 

 that the flame is not perfectly transparent. Three methods were 

 adopted for measuring the absorption, by comparing the light of 

 the edge and side of a flat flame, by reflecting the light a second 

 time through the flame by a mirror, and by viewing the electric 

 light through a large flame. The results lead to the coefiicient of 

 •80 for the absorption per centimeter in thickness. 



After having established the theoretical formulas whicli give 

 the effective brightness of the flame as a function of its volume 

 and coefficient of absorption, it appears that to satisfy the obser- 

 vations we must assume that the specific brightness increases a 

 little with the diameter. Multiplying then the specific brightness 

 by the volume, it appears that the total quantity of light increases 

 much more rapidly than the weight of oil burned; but as the 

 quantity of light absorbed increases still more rapidly, the light 

 increases a little less rapidly than the oil consumed, as experiment 



The second memoir relates to the nocturnal transparency of the 

 atmosphere. Observations are made three times every night by 

 the lighthouse-keepers, as to which of the adjacent lights are 

 visible. Combining the results for several years gives the per- 

 centage of nights on which each light is seen. The equation of 

 the range of visibility and a graphical construction serve to show 

 for each light in all cases what degree of transparency of the air 

 is needed to render the light visible. A curve may then be con- 

 structed with the transparency of the air and the visibility of the 

 lights as coordinates. From this it appears that during half the 

 year the coefi&cient of transparency per kilometer exceeds -91 in 

 the Atlantic and '932 in the Mediterranean. Similar cui-ves give 

 the transparency at different points along the coast, and during 



The third memoir treats of the apparent brightness of a light 

 caused by revolving the system of lenses employed with greater 

 or less rapidity. With a certain velocity, a flickering effect is 

 produced, but with an increased speed the light becomes steady 

 with an intensity one or two tenths less than would be obtained 

 by distributing the light uniformly around the horizon. — Cornptes 

 Rendus, Ixxxi, 1096. e, c. p. 



10. Mheric Force of Edison.— Yvo?. E, J. Houston, in an arti- 

 cle in the January number of the Journal of the Franklin Institute, 



