112 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



2. Refraction. 



Mascart has made a research upon the refractive power 

 of o-ases. A beam of light was sent through a collimator to 

 two plates of plate-glass connected together at right angles ; 

 the halves of the beam were bent right and left by refrac- 

 tion through the glass, then passed parallel through two 

 copper tubes containing the gases, and after refraction by a 

 second system of glass plates placed in reverse directions, 

 the halves were united again, and the beam passed through 

 a slit to a system of prisms, then to a telescope. If the press- 

 ure in one of the copper tubes varied, the phases of the two 

 parts of the beam became different, and from the number of 

 fringes displaced the refraction of the gas could be deter- 

 mined. The influence of pressure was examined, then the 

 refractive power for different wave-lengths, then the influ- 

 ence of temperature, and from these data the absolute re- 

 fractive power was deduced. The figures obtained range 

 from 0.1387 for hydrogen and 0.2706 for oxygen to 0.703G 

 for sulphurous oxide and 0.821 G for cyanogen. The refraction 

 of a mixture is the sum of the refractions of its components ; 

 but that of a compound gas is in general greater than that 

 of a mixture. 



De Waha has proposed a new and simple mode of measur- 

 ing the index of refraction of liquids. In a rectangular sflass 

 tank a piece of silvered glass is supported at any convenient 

 ano-le to one side, this side beino: also silvered to one half 

 its height. The tank being placed in the centre of a divided 

 circle, a beam of light from a narrow slit is allowed to fall 

 horizontally upon the side of the tank and normal to it, and 

 then upon the piece of silvered glass, the circle being turned 

 until this ray is also normal. The angle read off on the cir- 

 cle is the angle of the prism. The liquid to be examined is 

 then poured into the tank, and the beam of light is so adjust- 

 ed that its incidence in the liquid upon the silvered glass 

 surface is normal. In this condition of things, the angle of 

 refraction is the angle of the prism. Measuring then direct- 

 ly the angle of incidence, and dividing its sine by that of the 

 angle of the prism, the refractive index is obtained. 



Govi has suggested a mode of varying the focus of a mi- 

 croscope without touching the instrument or the object, and 



