1868. ] Astronomy. 375 
information respecting this part of the stellar motions. The law on 
which the inquiry proceeds may be thus illustrated :—If we ima- 
gine a powerful swimmer to urge his way rapidly against a series of 
advancing waves, it is evident that they will pass him more rapidly 
—in other words, they will seem narrower—than if he were at rest ; 
on the contrary, if he urged his way in the same direction as the 
waves, they would appear broader than they really are. Since the 
light of the stars reaches us in a succession of minute waves, it is 
clear that if we are approaching a star or receding from it, whether 
through the earth’s motion or that of the star, the ight waves 
will appear modified in length—in other words, the light’s refran- 
gibility will be altered. Thus the lines in the star’s spectrum will 
be altered in position, and will no longer coimcide with the corre- 
sponding lines in the spectra of terrestrial substances. Our space 
will not permit us to enter into an account of the methods which 
have been devised to enable spectroscopic analysis to deal with this 
very delicate research. At present we must content ourselves with 
exhibiting the two principal results of Mr. Huggins’s labours. He 
has succeeded in showing that the nebule are not approaching the 
earth or receding from it at a rate which is appreciable by his in- 
struments; but he finds that the bright star Sirrus—the only fixed 
star which he has yet had time to examine satisfactorily—is approach- 
ing the solar system at the rate of nearly 294 miles per second. 
Mr. Huggins has re-examined the spectra of several nebule. 
He finds that when the intensity of the spectrum of nitrogen is 
diminished by removing the induction spark in nitrogen to a suffi- 
cient distance, the whole spectrum disappears except the double line, 
which agrees in position with the bright line in the nebula. “ It 
is obvious,” he adds, “that if the spectrum of hydrogen were 
greatly reduced in intensity, the strong line in the blue, which cor- 
responds to one of the lines of the nebular spectrum, would remain 
visible after the line in the red, and the lines more refrangible than 
F had become too feeble to affect the eye.” We shall see presently 
that this view has been confirmed by an experiment made by 
Father Secchi. There seems reason for supposing that the light of 
the gaseous nebule is emitted by nitrogen and hydrogen. 
Mr. Huggins has also been able to confirm the observations 
made by Mr. Lockyer on the spectra of the umbre and penumbre of 
solar spots, and to obtain some new results of interest. He found 
that most of the dark lines of the solar spectrum were wider in the 
spectrum of the umbre. The lines F and C due to hydrogen were 
not stronger, however. No new lines were detected, nor were any 
of the lines of the normal solar spectrum wanting in the spectrum of 
the umbra. 
We hear that Mr. Lockyer is about to renew his observations of 
VOL. V. 2D 
