C. GENERAL PHYSICS. 149 



June, and July have given very accordant results in the 

 hands of Roscoe. 19 (7, VII., 202. 



NEW METHOD OF MEASURING THE VELOCITY OF LIGHT. 



A simple and possibly accurate method of measuring the 

 velocity of light is suggested by Mr. Burgue. A disk, turn- 

 ing very rapidly about its axis, is at each turn to be illumi- 

 nated by an intermittent and instantaneous light. A single 

 dark radial line on the disk will seem at rest, like the disk 

 itself. Now withdraw the source of light to a distance, and 

 the time the light takes to reach and illuminate the disk 

 will become greater, and the position of the radial line will 

 appear displaced to a new position, forming with its previ- 

 ous position a certain small angle, which will measure the 

 time of the light's passage over a given distance. 1 A, II., 

 262. 



GREAT FRENCH LIGHT-HOUSE AT LA HAVE. 



The great French light-house at La Have, near Havre, is 

 said to be the most magnificent establishment of its kind in 

 the world. The electric light was first used at this place 

 in 1863. The electricity is furnished by magneto-electric 

 machines, and the simple uncondensed beam of light is equal 

 to 4000 candles, and it seems to be the testimony of navi- 

 gators that this electric light is always seen, even in clear 

 weather, before the oil lamps nearer them. Its range of vis- 

 ibility is also correspondingly greater, the radius of the circle 

 lighted up being from five to ten miles greater than that of 

 first-class oil lamps. The difference between the two is, in 

 fact, similar to the comparison of a candle and a gas-light. 

 At some distance there is also a notable difference in their 

 aspects, the electric light appearing white and brilliant, the 

 other red and smoky. The superiority of the former is still 

 more manifest during foggy weather, since at such times, 

 even before perceiving the electric light, its presence is 

 marked by the illumination of the thick atmosphere sur- 

 rounding it, and its range thus increased. This is an impor- 

 tant advantage of the electric light, and may be of great 

 practical utility, as has, in reality, frequently been the case. 

 While its brilliancy gives it this superiority, its inferior 

 power of penetration diminishes the range of the electric 



