PHYSICS. f)()9 



(liiis (Ictermiue the total energy radiated, the light energy being simul- 

 taneously determined by eomparisou with a, standard candle. The heat 

 indications were found to be far more sensitive than tliose of the photom- 

 eter. Hence he suggests as a standard of light an incandescent strip 

 which radiates a definite amonnt of energy, this energy l)eing measured 

 at a fixed distance wliicli will best agree numerically with the absolute 

 system. (Am. J. ^cL, August, 1885, III, XXX, 128.) 



Frederick Siemens lias devised an important imj)rovement in gas 

 lighting, based on tlw a(loi)tion of the well-known regenerative principle. 

 In his 0}iini6n rooms should be lighted by means of indirect rays or 

 diffused light oidy, the source of light itself not being directly visible. 

 His lamp consists of four approximately spherical and concentric hoods 

 of sheet-iron or other suitable material so arranged that the products of 

 combustion travel downward between the second and third ami upward 

 between the third and fourth or outer one, while the air to be heated for 

 feeding the flame jiasses upward between the first and second and 

 through the first, filling this hood with very hot air. The products of 

 combustion pass through an opening in the top of the outer hood into a 

 cliimney. The concave surface of the first or lower hood acts as a reflec- 

 tor, and in its focus are placed one or more fish-tail burners of the usual 

 type. The gas is therefore burned in a highly heated air, the temper- 

 ature of which increases with that of the gas flames, the brilliancy of the 

 light increasing in the same ratio. Tests with this lamp showed that 

 the same burners burning the same amount of gas in the two cases gave 

 an average of 2-875 candles per cubic foot of gas consumed when re- 

 moved from the hoods and 7-74 candles i>er cubic foot when burned in 

 their proper place iu the lamp. {Nature, July, 1885, xxxii, 247.) 



Wolf has proposed another modification iu the well-known Foucault's 

 api»aratus for the velocity of light. His apparatus consists of two mir- 

 rors, one fixed, having a diameter of 0*2 meter, the other movable 5 centi- 

 meters in diameter, lioth are concave and spherical and have the same 

 radius of curvature. 5 meters. The source of light is a narrow aperture 

 cut iu the silver in the center of tUe large mirror. The pencil enuinating 

 from it and entirely covering the rotating mirror is reflected by the 

 latter and returns to form on the surface of the fixed mirror a movable 

 image of the aperture and of the same size. This is reflected back to 

 the revolving mirror, and by this the Foucault image is formed. If 

 now the mirror be rotated with sufficient speed there will be formed on 

 the fixed mirror a series of equal kinunous lines separated by e<iual 

 intervals, which will continue to increase their distance from each other 

 as the speed rises. These are Foucault images formed by multiple re- 

 flections, and the higher the image which can be measured the higher the 

 multiple of the Foucault deviation. The author is in hopes of meas- 

 uring the twentieth image, which would give a displacement of 35"'°'. 

 (C. 7^;., February, 1885, C, 303; Nature, April, 1885, xxxi, 517.) 



Michelson has publislied a note objecting to Wolf's assumption that 

 H. Mis. 15 39 



