Spectra of some of the Fixed Stars. 411 



stars which we have examined, the dark lines appear to be as 

 fine and as numerous as they are in the solar spectrum. The 

 great breadth of the lines in the green and more refrangible 

 parts of Sirius and some other stars, as seen in the less perfect 

 form of apparatus which was first employed, and which band- 

 like appearance was so marked as specially to distinguish them, 

 has, to a very great extent, disappeared ; and though these lines 

 are still strong, they now appear, as compared with the strongest 

 of the solar lines, by no means so abnormally broad as to require 

 these stars to be placed in a class apart. No stars sufficiently 

 bright to give a spectrum have been observed to be without lines. 

 The stars admit of no such broad distinctions of classification. 

 Star differs from star alone in the grouping and arrangement 

 of the numerous fine lines by which their spectra are crossed. 



6. For the convenience of reference and comparison, a few of 

 the more characteristic lines of twenty-nine of the elements were 

 measured with the instrument. These were laid down to scale, 

 in order to serve as a chart, for the purpose of suggesting, by a 

 comparison with the lines measured in the star, those elements 

 the coincidence of the lines of which with stellar lines was 

 probable. 



.For the purpose of ensuring perfect accuracy in relative posi- 

 tion in the instrument between the star-spectrum and the spec- 

 trum to be observed simultaneously with it, the following gene- 

 ral method of observing was adopted : — The flame of a small 

 lamp of alcohol saturated with chloride of sodium was placed 

 centrally before the object-glass of the telescope, so as to furnish 

 a sodium-spectrum. The sodium-spectrum was then obtained 

 by the induction-spark, and the mirror/ was so adjusted that 

 the components of the double line D, which is well divided in 

 the instrument, should be severally coincident in the two spectra. 

 The lamp was then removed, and the telescope directed to the 

 sun, when Fraunhofer's line I) was satisfactorily observed to 

 coincide perfectly with that of sodium in the induction-spark. 

 Having thus ascertained that the sodium lines coincided in the 

 instrument with the solar lines D, it was of importance to have 

 assurance from experiment that the other parts of the solar spec- 

 trum would also accurately agree in position with those corre- 

 sponding to them in the spectrum of comparison. When elec- 

 trodes of magnesium were employed, the components of the 

 triple group characteristic of this metal severally coincided with 

 the corresponding lines of the group b. C and F also agreed 

 exactly in position with the lines of hydrogen ; the coincidence 

 of several of the principal lines of iron was also observed. The 

 stronger of the Fraunhofer lines were measured in the spectra of 

 the moon and of Venus, and these measures were found to be 



