1904 - 5 .] On Prof. Seeliger’s Theory of Temporary Stars. 543 
where the observed phenomena may as well be explained by the 
revolution of the two stars round their common centre of gravity. 
In the introductory remarks to this paper I have laid consider- 
able stress on the fact that the observed displacements of the 
spectral lines are proportional to their wave-lengths, and independ- 
ent of the chemical nature of the emitting gas. I pointed out that 
this remarkable fact supports the view that the displacements are 
due to motions in the line of sight. Indeed, if an incandescent 
gaseous body is moved with a velocity v, its lines are displaced by 
an amount ± dX , so that 
+ dX = 
where V is the velocity of light ( = 300,000 km. per second) and X 
the wave-length of the line. This equation holds also if the body 
consists of a mixture of gases moving in the line of sight with a 
common velocity v. Hence any line of the spectrum emitted by 
these various gases will be displaced by an amount 
±dX = const, x A, 
i.e. the displacement depends solely on the wave-length. Professor 
Becker's elaborate measurements confirm this statement in every 
respect. I should like here to supplement his important con- 
clusions, which bear out so admirably the theoretical results of 
this communication, by a few similar measurements published by 
Messrs Campbell and Wright in the 8th Bulletin of the Lick 
Observatory. I begin with the displacements of the absorption- 
bands. The following table contains in the first column the lines 
measured and the elements to which they belong, in the second 
and third columns the observed and computed displacements 
towards the violet. The values of the third column have been 
computed from the formula : — 
- dX= 0*0046 x A 
Displacement 
Observed. Computed. 
Calcium j 
m ) ( 
Hy V Hydrogen < 
H p) I 
D Sodium 
- 17 t.m. 
-18 
- 16 
- 18 
-19 
- 19 
-19 
-19 
-24 
-22 
-27 
-27 
