529 
One should be mindful both of objective and subjective errors in 
this- connection. 
Let us imagine two lines, bright in the negative (dark in the 
original spectrum), which, if standing isolated, would each of them 
show symmetrical distribution of the light, but which are in fact 
situated so near one another that they partially overlap; then the 
maxima of intensity will (as an objective effect) be at a smaller distance 
from each other than the real centres of the lines. This would become 
obvious when the intensity in the system is recorded by means of the 
micro-photometer, supposing the real distance of the cores of the 
lines to be known. 
On the other hand one would be inclined to over-estimate the 
distance between the maxima owing to the contrasts being weakened 
in the intervening space. This is a subjectiwe effect. 
It is not easy to presume which of these two opposite influences 
predominates‘). As this is a problem of high importance whenever the 
exact distance between the components of close double lines has to 
be determined, it is at present being made a subject of special 
inquiry in the Utrecht physical laboratory. 
But whatever may be the result of that investigation, it can easily 
be shown that the mutual influence revealing itself in the above 
mentioned observations published by Apams and Kversuep and Royps, 
is almost independent of the errors of estimation here considered, 
and that the phenomenon cannot therefore be ascribed to such errors. 
Indeed, let us suppose that in the spectrum of the sun’s centre 
the exaggeration of the distance between the components of a certain 
pair of lines be due to an error of estimation. 
The distance be e.g. 0,3 A, the apparent exaggeration caused by 
this nearness 0,003 A. 
Let us next consider the same pair in the spectrum of the sun’s 
limb. There both components are perhaps slightly shifted with respect 
to their positions in the centre spectrum; but their distance can 
scarcely be altered thereby more than, say, 1°/, of its original value 
of 0,3 A. Consequently the influence which the proximity of the 
1) Sr. JorN considers the latter influence the most important, and supposes it 
to be the principal cause of the fact that in RowLAND’s wave-length tables the 
distances between the components of narrow pairs of lines are greater than they 
should be according to measurements made on Mt. Wilson. He therefore calls the 
differences “systematic errors” in RowLAND's wave-length determinations (Astroph. 
Journ. 44, 16 and 265 (1916); Mt. Wilson Contrib. N°. 120 and 123). This opinion 
was contested by one of us in a communication to the Amst. Akad. 25, 1245 
(1917). Cf. also; Archives néerland. Ill A, Tome V, 122—126 (1918). 
