Spectra of some of the Fixed Stars. 407 



brighter stars could be seen. The remeasuring of those already 

 described by Fraunhofer and Donati, and even the determining 

 the positions of a few similar lines in other stars, however, would 

 have been of little value for our special object, which was to 

 ascertain, if possible, the constituent elements of the different 

 stars. We therefore devoted considerable time and attention to 

 the perfecting of an apparatus which should possess sufficient 

 dispersive and denning power to resolve such lines as D and b 

 of the solar spectrum. Such an instrument would bring out 

 the finer lines of the spectra of the stars, if in this respect they 

 resembled the sun. It was necessary for our purpose that the 

 apparatus should further be adapted to give accurate measures 

 of the lines which should be observed, and that it should also be 

 so constructed as to permit the spectra of the chemical elements 

 to be observed in the instrument simultaneously with the spectra 

 of the stars. In addition to this, it was needful that these two 

 spectra should occupy such a position, relatively to each other, as 

 to enable the observer to determine with certainty the coincidence 

 or non-coincidence of the bright lines of the elements with the 

 dark lines in the light from the star. 



Before the end of the year 1862 we had succeeded in con- 

 structing an apparatus which fulfilled part of these conditions. 

 With this some of the lines of the spectra of Aldebaran, a Ono- 

 nis, and Sirius were measured; and from these measures dia- 

 grams of these stars, in greater detail than had then been pub- 

 lished, were laid before the Royal Society in February 1863. 

 After the note was sent to the Society, we became acquainted 

 with some similar observations on several other stars by Ruther- 

 furd, in Silliman's Journal for 1863*. About the same time 

 figures of a few stellar spectra were also published by Secchif. 

 In March 1863 the Astronomer Royal presented to the Royal 

 Astronomical Society a diagram in which are shown the positions 

 of a few lines in sixteen stars J. 



Since the date at which our note was sent to the Royal Society 

 our apparatus has been much improved, and in its present form 

 of construction it fulfils satisfactorily several of the conditions 

 required. 



§ II. Description of the Apparatus and Methods ofObse 

 employed. 



4. This specially constructed spectrum-appara f 

 to the eye-end of a refracting telescope of 8 inc 1 

 10 feet focal length, which is mounted equa^ 



* Vol. xxxv. p. 71. 



f Astronomische Nachrichten, No. 1405, V 



% Monthly Notices of the Royal Astror 



2E' 



