Rays emitted by Glowing Platinum. 453 
\ ox ea when the lens is used. The a P entes distance 
i 
this scale. The scale was of boxwood and the half millimeters 
were marked by fine lines. The following table gives the 
angles corresponding to linear displacements of , 4, ete. milli- 
meters. Hach result is the mean of six readings. 
Tasie IDL. 
Ss a 
0-°125mm 1 
0-250 32 24 
0°375 44 64 0 
0°500 55 22 12 
0°625 64 46 12 
0-750 72 28 12 
If in formula (5) ¢ is substituted for ¢ and values from the 
ie table for S and 7, we obtain, » being known, from the 
nation, 
Q sin*z dhe! sin’z cos?\ 
80/1 — 88 = esini (4/1 . ) (6) 
the numerical solution, 
€ = 1030977". 
All the data necessary to the measurement of the distance a, 4, 
Were thus at hand. The distance a), (fig. 5) is. however, 
4,5,-+mm,. Now the points m and m, are coincident in the 
field of the opthalmometer, appearing to lie at m,; and their 
real distance can be measured by simply observing the double 
mages of the above-mentioned seale as they appeared in the 
