1868.] 



Mr. W. Huggins on the Spectra of the Sun. 



385 



was to degrade the refrangibility of the dark hne in Sirius by au amount 

 of wave-length equal to 0'109 millionth of a millimetre. 



If the velocity of light be takm at 185,000 miles per second, and the 

 wave-length of F at 486*50 millionths of a millimetre, the observed altera- 

 tion in period of the line in Sirius will indicate a motion of recession 

 between the earth and the star of 41*4 miles per second. 



At the time of observation, that part of the earth's motion which was 

 in the direction of the visual ray, was equal to a velocity of about 12 miles 

 per second from the star. 



There remains unaccounted for a motion of recession from the earth 

 amounting to 29*4 miles per second^ luhich we appear to he entitled to 

 attribute to Sirius. 



Reference is made to the inequalities in the proper motion of Sirius ; 

 and it is stated that at the present time the proper motion in Sirius in 

 declination is less than its average amount by nearly the whole of that 

 part of it which is variable, which circumstance may show that a part of 

 the motion of the star is now in the direction of the visual ray. 



Independently of the variable part of its proper motion, the whole of 

 the motion wdiich can be directly observed by us is only that portion of 

 its real motion which is at right angles to the visual ray. Now it is pre- 

 cisely the other portion of it, which w^e could scarcely hope to learn from 

 ordinary observations, which is revealed to us by prismatic observations. 

 By combining both methods of research, it may be possible to obtain some 

 knowledge of the real m.otions of the brighter stars and nebulae. 



Observations and comparisons, similar to those on Sirius, have been 

 made on a Canis Minoris, Castor, Betelgeux, Aldebaran, and some other 

 stars. The author reserves the results until these objects have been re- 

 examined. It is but seldom that the atmosphere is favourable for the 

 successful prosecution of this very delicate research. 



§ V. Observations of the Sun. 



The author has observed the sun with three distinct objects in view : — 



1 . He has sought to discover if the spectrum of the light from the less 

 luminous part of the sun near the limb, differs in any respect from that of 

 the light from the central parts of his disk. 



2. He hoped to obtain a view of the red prominences visible during a 

 solar eclipse by reducing the light from our atmosphere by dispersion ; 

 for, under these circumstances, if the red prominences give a spectrum of 

 bright lines, these lines would remain but little diminished in brightness, 

 and might become visible. 



His observations in these two directions have been hitherto unsuccessful. 



3. He proposed to seek to gain from an examination of the spectra of 

 the umbrae and penuni])r8e of solar spots, some information as to the 

 nature of these phenomena. He has successfully applied the large spec- 

 troscope, already described, to the light from the umbra of a spot. 



