. much smaller than 5 or 6 atmospheres, there will be no 
whole effect. 
Similar considerations apply to another general result of recent 
otovations, viz. to certain systematic differences existing between 
of the centre and that of the limb o the disk. 
Boisson and Fabry resume the facts as follows ): 
1 Ilya un changement d’aspect pour certaines xaies. Pour les 
fortes rates la penombre est affaiblie dans le spectre du bord. Parmi 
les autres raies, quelques-unes sont renforcees on 
bords du disque, et le changement est en general de memesensque 
sr,- *—- 
bottis un leger accroissement de longueur d’onde; ses mesures ont 
ete faites sur deux raies rouges du fer, en comparant leurs positions 
a cedes de deux raies telluriques voisines. II a trouve un deplacemen 
^Using^ theiT hiterferential method Buisson and Fabhy examined^nto 
14 lines of various metals (intensities 2 to 6 on f °™ LAN “ " ^ 
and found Ham’s result .confirmed: a displacement to the red va^in 
between 0,004 and 0,006 Angstrom units, when passing fromi th 
centre to the limb. (Two vanadium lines were not displaced). M « re °* e ' 
those same lines appeared to be about 0,010 Angstrom units * der 
at the limb than at the centre of the disk. So we may take it as 
if the widening affects chiefly the red-facing side of the lines. 
If one wishes to interpret this phenomenon too y means 
pressure effect - as the discoverers did - one must adm. that 
deeper layers, in which the pressure is higher, contnbute relaUvdj 
more to the formation of the absorption lines near the limb than 
near the centre of the solar disk. , . _ 
We will not dwell on various difficulties, encountered m develop ng 
this idea; probably it will be possible to remove them by introducing 
additional hypotheses concerning the thickness of t e ayers, 
temperature and other physical conditions of the absorbing vapours 
At all events it is unnecessary to ascribe the above differences 
between the spectra of the central and the marginal parts of he 
disk entirely to pressure; for anomalous refraction w ic un 
tedly comes into play - acts exactly in such a way, that in the 
\) Buisson et Fabry. Comptes rendus L _28 juin 
