( 250 ) 
are dh ; 
as separate lines. For these radiations = = =4,5.10-% or r= 222000 
and hence g, rather smaller; calculation gave g; = 3,6.10-#, 
Using the green line of thallium ") I extremely easily distinguished 
dh mes 
the faint radiation at a distance qe 21.10-° from the principal 
radiation, but I could not see as a separate line the one determined 
by <= = 370-4, 
Hence g, exceeds 3.10—* but is smaller than 21.10—°. 
Indeed for the thallium radiation (5440) 
i 
= (eee 
For the green (5086) line of cadmium it was just possible to 
see that this line is a double one. The distance of the components 
Ih 
is according to FABRY and PerROT = == 5.10-§,2) Hor A= 50860 
calculate g:=3,2.10—-°. Hence with the mentioned echelon it is 
possible to almost reach the limit of the theoretical resolving power. 
§ 3. Perhaps the best series of tests of gradually increasing 
difficulty can be obtained by observation of the change of spectral 
lines in magnetic fields of gradually increasing intensities, a Nicol 
between source and apparatus being used in order to reduce the 
complexity of the radiation. In this manner all values between 
e.g. 0.001 A.U. to about 1 A. U. can be obtained. Corresponding 
herewith are the values g;=0,2.10-® and r— 5000000 resp. 
qt = 200.10-® and r= 5000. The performances of echelons and 
interferometers and of ordinary spectroscopes with a few glass prisms 
lie between the limits indicated. This test I have not yet applied 
systematically to the mentioned echelon. 
In order however to show its fitness I will use some cbservations 
of Lord BuyTHswoop and Dr. Marcuanr®). In their 86 „Results 
obtained of the Zeeman Effect on the Chief Lines of the Mercury 
Spectrum” p. 397 these authors communicate observations with an 
1) Fasry et Peror. Ann. de Chim. et de Phys. (7) 16. p. 134. 1899, 
‘Veli cap. late 
3) Phil. Mag. Vol. 49. p. 384. 1900. 
ee ed a 
+ 
