Physics. — Mutual Influence of Neighbouring Fraunhofer Lines” *). 
By Prof. W. H. Junius. 
(Communicated at the meeting of January 29, 1921.) 
If the hypothesis holds good that the darkness of Fraunhofer lines 
is not a pure absorption effect — as it is commonly supposed to be — 
but chiefly due to anomalous dispersion (showing itself both in mole- 
cular diffusion and irregular ray-curving), we may expect on theo- 
retical grounds?) that neighbouring Fraunhofer lines will, as arule, 
seem to repel each other. If, now, such a mutual influence is 
actually found to exist, a mighty support will thus be given to the 
said interpretation of the solar spectrum, as long as it remains 
impossible to explain that phenomenon on the basis of the current 
view that one is dealing with mere absorption lines. 
In a communication on “The general relativity theory and the 
solar spectrum”®) we have made use of the already reliable and 
striking results obtained in a preliminary research on the manifes- 
tations of mutual influence of Fraunhofer lines as appearing in the 
limb-centre displacements measured by AbAms*) about the year 
1910. At my request Dr. P. H. van Crrrerr and Dr. M. Minnagrt 
have, however, once more examined the same data with the utmost 
care, using still more rigorously defined criteria, in order that every 
trace of bias might be avoided in selecting the lines. Besides, the 
investigation has been extended over the observation son limb-centre 
displacements published by EversHeD, Narayana Ayyer and Royps °) 
in 1914—191L6. It will appear that this extension of the field has 
led to a considerable corroboration of the former inferences, so as 
to put the existence of mutual influence practically beyond doubt. 
Care has been taken, of course, that during the act of selecting 
lines that would probably be influenced, one was ignorant of the 
observed displacements. Basing ourselves on the conception how, 
1 This paper is an abstract of an ampler article that has since appeared in the 
Astrophysical Journal 54, 92 (1921). (Note, added January 1922). 
2) Cf. Astroph. Journ. 43, 49—53 (1916). 
3) W. H. Junius and P. H. van Cittert. These Proc. 23, 522 (1920). 
4) W. S. Apaus, Astroph. Journal 31, 30 (1910); Mt. Wilson Contrib. No. 43. 
5) EversHep and Royps, Kodaik. Bull. 39 (1914); Narayana Ayyer, Kodaik. 
Bull. 44 (1914); Royps, Kodaik. Bull. 53 (1916). 
72 
Proceedings Royal Acad. Amsterdam. Vol. XXIII. 
