308 
SCIENTIFIC SUMMARY. 
ASTRONOMY. 
l^OTION of Sirius in Space. — Mr. Huggins lias led tlie way in a process 
of inquiry which promises results of the utmost value and interest. 
It will be remembered by many of our readers that M. Doppler suggested, 
several years ago, the possibility that the colours of the fixed stars, and more 
particularly the colours of the double stars, may be partly due to motions of 
recess or approach which these stars may have with respect to the earth. He 
pointed out that the waves of light proceeding from a star would be apparently 
shortened if the star were approaching the earth very rapidly, and vice versa. 
In other words, the spectrum of a star would be shifted from the red towards 
the blue end of the spectrum in the case of a star rapidly approaching the earth, 
and from the blue towards the red end of the spectrum in the case of a star 
rapidly receding from the earth. But Doppler failed to notice that no effect 
could be produced upon the colour of a star by changes of this sort. For at 
either end of the visible spectrum there exists an invisible prolongation, due 
to waves longer or shorter than those which the eye is able to appreciate as 
light. Hence the rapid motion of a star, either towards or from the earth, 
would in reality produce no effect on the several appearances of the spec- 
trum, since one or other end of the visible spectrum would become invisible, 
while a corresponding portion of the invisible part beyond the other end of 
the spectrum would be rendered visible, the apparent colours remaining 
unchanged. And further, the rate of motion required to produce a change 
of colour, even in the imaginary case of a monochromatic star, would be far 
greater than we are justified (on any evidence we have) in assigning to the 
fixed stars. A velocity of 100 miles per second may be looked upon as 
absolute rest, in comparison with the enormous velocity of light ; and a 
velocity ten times as great would probably be required to produce any 
appreciable change of colour in monochromatic light. 
But Mr. Huggins has applied M. Doppler’s principle in a far more satis- 
factory manner. The presence of dark lines in the spectra of the fixed stars, 
and of bright lines in several of the nebulae, and the known fact that these 
lines correspond to those of certain terrestrial elements, suggested the pos- 
sibility of ascertaining whether any minute variation in the position of 
certain well-known lines might not be found to give evidence of stellar or 
nebular motions of recess or approach. 
After a long process of experiment and observation, Mr. Huggins has 
