217 
from the zero point. The blackening is proportional to this; hence 
when f is a factor of proportionality, the following equation will 
hold for the lower band: 
Tif ZEE At ELD) 
Analogously 
Ll Zi Velhanern ee 
for the upper band when on it that point is chosen as zero point 
N’ that was in Q’ when the prism passed through the position 
/'=—0, hence when l= — d according to (14). 
Now equation (14) passes into: 
my, my 
fLld).= JE (m) dm + 2 fx (m)cos4almdm. . . (17) 
ms mna 
2 (el)= afs (m) dm —2 fx (m) sin An lmdm . . . (18) 
The functions fZ and fZ' oscillate round the same constant value: 
my 
2 fund, when / and /' are increased; they will asymptotically 
ug 
my, my 
a] 
approach this value, for Jam cos 4a lmdm and f x0 sin da mdm 
De / ma 
become zero for large values of / and /' on account of the continual 
reversal of the sign of the cosinus and the sinus, even when we 
have only to integrate over a small interval with respect to m. 
According to equation (17) the ordinate Z will reach the greatest 
maximum for /=0. This can be sharply determined from the course 
of the Z curve, when we have to do with multichromatic light. 
The bottom of this ordinate is the zero point MN. This operation is 
equivalent to the adjustment at the white point in the interferometer 
of MicueLson, when white light is used, and when we want to make 
the movable mirror coincide with the plane of reference. The adjust- 
ment can of course much more accurately be effected graphically 
than visually. 
Mi 
AS Zaman afs (m)dm, it follows from equations (17) and (18) that: 
Mag 
mi 
2 fx () can dae Im dm =f Z (Cl) — 2 Ze davies, GEO) 
Me 
