PHYSICS. 363 



toward the central glass of tbe refractometer, and the latter adjusted 

 by screws till the light passed centrally down both tubes and then the 

 right-angled prism at the farther end adjusted till the light returned 

 and was reflected into the telescope, where generally two images were 

 -observed. These were made to coincide and the fringes at once ap- 

 peared. At a given signal the current of water was turned on, moving 

 in opposite directions in the two tubes. The width of the central fringe 

 was measured micrometrically and the displacement in one direction- 

 The current of water was then reversed and the displacement again 

 measured. This displacement was nearly the width of an entire fringe. 

 The velocity of the water being determined, the value sought is easily 

 calculated. The authors announce as the result of their work that the 

 conclusion obtained by Fizeau is essentially correct, and that the lu- 

 miniferous sether is entirely unaffected by the motion of the matter which 

 it permeates. (Am. J. Sci., May, 1886, III, xxxi, 377.) At the next 

 meeting of the French Academy Cornu thus spoke of the foregoing 

 research : "Leur travail C0U9U dans I'esprit le plus 61eve, execute avec 

 ces puissants moyens d'action que les savants des fitats-Unis aiment a 

 deployer dans les grandes questions scientifiques, fait le plus grand hon- 

 neur a leurs auteurs." Fizeau himself also added his commendations 

 (C. R., May, 1886, cii, 1207). 



The British Association committee on standards of white light have 

 made a preliminary report. An examination of existing standards, they 

 say, convinces them that the standard caudle as defined by act of Par- 

 liament is not in any sense of the word a standard. The French "bee 

 Carcel" is also liable to variations; and with regard to the molten plati^ 

 num standard of Violle, it seems that the difHculty of applying it is so 

 great as to render its general adoption almost impossible. As to pro- 

 posed standards, the .majority are satisfied that for all the present com- 

 mercial requirements the iientane standard of Vernon Harcourt, which 

 has no wick and consumes a material of definite chemical composition, 

 is, when properly defined, an accurate and convenient standard, and 

 gives a much more accurate illumination than the standard candle. As 

 to future researches, the electrical direction seems promising, and a 

 standard of white light might be established defined somewhat as fol- 

 lows : A unit of light is obtained from a straight carbon filament, in 

 the direction at right angles to the middle of the filament, when the 

 resistance of the filament is one-halfof its resistance at 0° C, and when 

 it consumes 10^ C. G. S. units of electrical energy per second. (Nature, 

 January, 1886, xxxiii, 236.) 



Koeuig has described Weber's photonieter to the Berlin Physical 

 Society. It consists in the main of a small benzine lamp which is 

 placed in a tube in front of a mirror and which illuminates a milk-glass 

 ]date adjustable in the tube. From this plate the light is carried to a to- 

 tally reflecting prism and thence into the eye-piece, where it lights up one- 

 half of the field of vision. The other half receives light from another milk- 



