Address of Sir William Thompson. 285 
More of the lines in the spectrum of the star, with a line or 
in the spectrum of sodium, or some other terrestrial sub- 
stance, and then (by observing the star and the artificial light 
Simultaneously by the same spectrosco 
parisons between the positions of the dark lines in the prisma- 
Ue spectrum and in his own 
debaran, a Orionis, 6 Pegasi, Sirius, @ Lyre, Ca lla, “ 
Mirus, Pollux, Castor (which they had observed rather for the 
rov 
great a velocity as 315 es per second to or from the 
h, whi ° “ 
corrected for the velocity of the Earth at the time of the obser- 
vation, gave a velocity % Sirius, relatively to the Sun, amount- 
