PHYSICS, I'KiHiUKSS OF, IN 1893. 



C19 



neriments on tin- percentage of light reflected 

 by \ari<>us diirii>iiig Mirfaces rcMilled us follow : 



MATKKIAL. 



I'r oral, of light reflected. 

 80 



Cartridge paper 



Tru-iliK rli'tli 



Tracing impcr 



( >rdinary mirror 



( >nlin:iry foolscap 60 to 70 



Tissue paper (one thiokncwM. 

 Tissue p:i|.T (two thick nesses). 



Yollow wall paper 



Blue paper 



Dark-brown \K\\n-r 



Yellow puinu-d wall 



Uhi.-k doili 



Block velvet 



40 



40 

 25 

 18 

 '20 



u 



0-4 



ami 1-2053. Olszowski and Witkowski (Cracow 

 Academy, quoted in "Nature," April 27) have 

 determined ilu: refractive index of liquid oxygen 

 \>y immersing in it a double glass plate inclosing 

 a layer of air, turning it, and measuring the 

 bright interference fringes at the borders of the 

 lidd of total reflection. They find the rela- 

 tive index to lie 1*2232 and the absolute index 

 l-^.'J"). In the same experiments they ascer- 

 tained that the maximum absorption of the 

 liquid i> lift ween A. = 577 and X = 570 where it is 

 84 to Hi) per cent, for a thickness of one milli- 

 metre. P. Joubin (Paris Academy of Science, 

 Dec. 12) thinks that he has established the law 



PHOTOGRAPH OK RIFLE BVLI.ET IN MOTION. WITH ACCOMPANYING SOUND WAVES. 



The long object at the left is the bullet, moving from right to left. The irregular thick black linos just in front 

 of it and some distance behind it are the wires between which it has just closed the electric circuit that caused 

 the spark that took the picture. The waves are seen stretching diagonally back from the front and rear ends 

 of the bu|let. Each consists of a dark line with a light line within it. showing that both waves are waves of 

 compression. The horizontal line near the bottom of the photograph and the V-shaped one at the top are 

 .reflectors. It will be seen that the waves are reflected like all similar disturbances, and that in the reflected 

 wave the position of the dark and light lines is reversed, the wave of compression being reflected as a wave 

 of rarefaction. 



Iff fraction. Kayser and Rungo (Berlin 

 Academy of Science) have measured the refrac- 

 tive indexes of the atmosphere for every part of 

 the spectrum by the deflection caused by a prism 

 introduced between a Rowland grating and a 

 sensitive plate. For the normal temperature 

 and pressure the indexes are as follow: 



A. 1-000-2902 P, 1-00059^0 II, 1-000297B 

 D, 1- 000*29 19 O, 1-000*2909 N. l-OniweiiO 



1-0008217 



Livcingand Dewar (" Philosophical Magazine.'' 

 October) rind that the refractive indexes of liq- 

 uid nitrogen and liquid air are respectively 1-^-Jti 



that the index of refraction is proportional to 

 the square root of the quotient of the molecular 

 weight by the number of constituent atoms. 



l>i*l>?rsion. Rubens and Snow ( Philosoph- 

 ical Magazine," January) find that the disper- 

 sion of fluorite is exceedingly small in the visible 

 spectrum and very great in the infra-red, so that 

 it is peculiarly adapted to the production of heat 

 spectra. It is. moreover, easily worked, and has 

 a very permrfhent surface. 



Absorption. G. B. Rizzo (Turin Academy) 

 has measured the absorption of light by plati- 

 num at different temperatures, a transparent 



