i)K. MILLEE^S EXETER LECTURE. 345 
as enumerated in the following table, are present in the atmo- 
sphere of the sun, viz. : Aluminum, barium, cadmium, calcium, 
chromium, cobalt, copper, hydrogen, iron, magnesium, manga- 
nese, nickel, sodium, strontium, titanium, zinc. 
By concentrating the light of the brightest fixed stars with a 
powerful telescope, a point of light of sufficient intensity may be 
obtained to enable its spectrum to be examined. It is neces- 
sary first to open oiit this point into a narrow line of light ; and 
this is effected by the use of a cylindrical lens, which spreads 
the light out in one plane only. The telescope must be made 
to follow exactly the apparent motion of the star in the heavens ; 
and in the telescope, exactly at the focus of the object-glass, a 
narrow slit, not wider than a fine hair, is placed. The light of 
the star must be kept perfectly steady on this slit, and then be 
examined through a small spectroscope, which is attached to the 
telescope and follows its movements. A special apparatus is 
also connected with the instrument for producing sparks from 
the particular metals which it is desired to compare with the 
lines in the star spectrum.* The diagram to which I now call 
your attention represents the star spectroscope employed by Mr. 
Huggins and myself in these difficult and fatiguing observa- 
tions. Only the brighter stars have as yet been examined; 
eight or ten pretty fully, others less perfectly. It is, of course, 
impossible to render such observations visible to more than one 
person at a time, and then only under particularly favourable 
Fig. 13. 
circumstances, and when the star is in a suitable position in the 
heavens. I have, however, here some photographs of careful 
* A figure and detailed description of this iustrunient was given in tli 
April number of this Revimo, p. 142, fig. 7, Plate XLII. 
