308 Measurement of the Refractive Index of Liquids, 



Fiff. 3. 



Second method of determining p for a liquid. 



Arrange two pLmo-convex lenses so as to form a telescopic 

 system of minimum aberration, that is so that a parallel 

 incident beam may emerge as a parallel beam. Let the 

 outer faces of the lenses be of equal curvature R, and let t be 

 the thickness of each lens, and // the refractive index of its 

 material. Then the equations representing the successive 

 refraction of a parallel beam through the two surfaces of the 

 first lens are 



/*'V x =-B(m'-1), 



jiV.^'Vi/u+ViO. 



Vj and V 2 having the usual meanings, and \x being the 

 refractive index of the medium adjoining the plane surface of 

 the lens. This gives 



Hence, if d = distance between the plane-faces of the lenses, 



Rd-fi'-mji'- 1)' 



