100 



THE INTERFEROMETRY OF 



TABLE 24. Submergence of glass convex lenses in mer- 

 cury-potassic iodide solutions. Thickness of the trough 

 inside, 0.293 cm. Focal power, i diopter. Sodium line. 

 Glass, 5=4.5X10-"; 2/X 2 = 0.0262. 



x Focal power 2 diopter, xx Washed ellipses. / Concave lens. 



In both these series the trough was not fixed with adequate rigidity, so 

 that errors crept in from this source. Nevertheless, if the data are con- 



63 -55 



structed graphically (ni+K for solution as abscissa and for submerged 

 glass as ordinate), the results (figs. 65 and 66) show a very definite trend 

 and show also that slight interpolation would be possible. It would be 

 hasty, however, to infer that the intersection at a of the graph for submerged 

 glass with the line at 45 through the origin is the index of refraction of the 

 glass, in so far as the data for the liquid are trustworthy. The method 

 seems to be deserving of notice; but before discussing the matter further 

 it will be necessary to determine the dispersion involved in B. 



53. Dispersion constants. As shown in 51, the constant Bis found by 

 passing the center of ellipses between Fraunhofer lines, both in the presence 

 and absence of the plate to be tested. In the case of liquids the empty and 



