214 
the focal line is passed, (the path is seemingly shortened by this) the 
phase-difference of the interfering rays at U becomes: 
Aan VT + An {x(q—p—d) + d} + ; or 4 a Um + 5 
when we put: 
wilg Pd SUS ae en Pe mie EK LO) 
and : 
VI el RE) 
This phase-difference also exists between the rays 1r and 2d, 
which follows from the figure and from the foregoing remarks. 
In analogy with equation (3) the intensity for compound light 
now becomes: 
my my 
J) = 2 fix (m) dm + 2 fi (m) cos (43 Um + =| dm or 
Mo ma 
my my 
N= fx (m) dm — 2 fx (m)sin4dalimdm or... . (12) 
+a 
TULES 2 fo (e) da — 2 sin Aar Um C(l’)—2cosda lim S(l’) . (13) 
=a 
C and S no longer occur in the combination of equation (4). 
This is owing to the cylinder lenses. J’ will henceforth be the inten- 
sity measured in Q’, hence with the modified interferometer, J 
that with the unmodified interferometer. A similar difference will 
also be made between 7 and 7’: / refers to the original interfero- 
meter, and is the distance from the shiftable mirror to the reference 
plane; 7’ is the quantity that characterizes the position of the movable 
prism in the new interferometer, and controls the intensity. In order 
to calculate C and S for a given value /, from equations (4) and 
(13), we should have to place the mirror in one interferometer, the 
prism in the other in such a way that the quantities / and /’ both 
acquire the value /,. This would be practically unfeasible, when one 
worked with the two interferometers separately. We shall, therefore, 
try to combine them to one instrument, in which the quantities / and 
l’ both oceur, and are therefore equal. This seems to me practically 
no more feasible than the adjustment of the two interferometers to 
one and the same value /, of the parameters. | have, however, 
