270 



NA TURE 



\Jan. 22, 1 1 



Vega, a Cygni, a Virginis, 17 Ursae Majoris, a Aquilre, 

 Arcturus, /3 Pegasi, Betelgeux, Capella, a Herculis, Rigel, 

 and a Pegasi. Also of the planets Jupiter, Venus, and 

 Mars, and of different small areas of the moon. 



The spectra of Sirius, Vega, a Cygni, a Virginis, r; Ursa: 

 Majoris, a Aquilae and Arcturus are laid down in the map 

 on the scale of M. Cornu's map of the ultra-violet part of 

 the solar spectrum. 



The stellar spectra extend from about G to O in the 

 ultra-violet. 



Six of these spectra belong to stars of the white class. In 

 1864 the author pointed out the features in common in the 

 visible spectra of these stars. These photographs present a 

 remarkable typical spectrum consisting of twelve strong 

 lines (seven only of these were given in the preliminary 

 note in 1876). The least refrangible of these is coincident 

 with the hydrogen line (y) near G. The second with // 

 also a line of hydrogen. The third with H. K if present 

 at "all, is thin and inconspicuous. 1 



These lines, H and K, are coincident with lines in the 



calcium spectrum, and are usually attributed to the 

 vapour of this substance. Now there is another pair of 

 strong lines in the spectrum of calcium, which in M. 

 Cornu's map have the wave-lengths 3736-5 and 3705-5. 

 There are no strong lines in the white stars coincident 

 with these lines. A glance at the map will show how 

 remarkable is the arrangement in position of these twelve 

 typical lines. They form a great group in which the 

 distance between any two adjacent lines is less as the 

 refrangibility increases. It is at once suggested that 

 they are connected with each other and represent probably 

 one substance, and two at least belong to hydrogen. 



It should be stated that the continuous spectrum ex- 

 tends in the photographs beyond S, but no lines can be 

 detected beyond the twelfth line at X 3699. For the sake 

 of convenience of reference the author distinguishes these 

 lines by the letters of the Greek alphabet in the order of 

 refrangibility, beginning with the first line beyond K of 

 the solar spectrum. The wave-lengths of these lines are 

 as follows : — 



Photographic Spec 



Hydroge 



1. G 434° 



2. h 4101 



3. H 3968 



4- « 38S7-S 



5- 3834 



6. y 3795 



7- 8 3767-5 



8. <r 3745 



9- £ 373° 



10. 1 37I7-5 



ii- 6 3707-5 



12. 1 3699 



In all these stars the line K is either absent or very 

 thin as compared with its appearance in the solar spectrum.- 

 In the spectrum of Arcturus, which belongs to the solar 

 type, this line exceeds in breadth and intensity its con- 

 dition in the solar spectrum. The white stars may, 

 therefore, be arranged in a series in which the line K 

 passes through different stages of thickness, at the same 

 time that the typical lines become narrower and more 

 defined, and other finer lines present themselves in in- 

 creasing numbers. Arcturus seems to present a spectrum 



1 The author refers to Mr. Lockyer's paper, Proceed. R. S., No. 16S. 

 1376, in which he suggested that photographs of the spectra of the brighter 

 stars might show modifications of this character of the lines of the calcium 

 spectrum, and that such modifications would confirm his views on the 

 dissociation of this substance. Reference is also made to Proceedings R.S., 

 December, 1878, Fig. 1, where Mr. Lockyer gives a fuller statement of his 

 views on this and other points in connection with different classes of spectra 

 of the st .rs. 



- Messrs. Dewar and Liveing have ound in their experiments similar 

 relative changes of intensity of the lines of calcium corresponding to H and 

 t spectrum of calcium. 



rum o£ a Lyra. 



on the other side of that of the sun in the order of changes 

 from the white-star group. 



The spectra of the planets were taken on the plan sug- 

 gested by the author in 1864, in which the planet's 

 spectrum is observed or photographed together with a 

 daylight spectrum. These photographs show no sensible 

 planetary modification of the violet and ultra-violet parts 

 of the spectrum of the planets Venus, Mars, and Jupiter. 



Numerous spectra of small areas of the lunar surface 

 have been taken under different conditions of illumination, 

 and during eclipses of that body. The results are wholly 

 negative as to any absorptive action of a lunar atmo- 

 sphere. 



The author is preparing to attempt to obtain by photo- 

 graphy any lines which may exist in the violet and ultra- 

 violet spectra of the gaseous nebula?. He also points out 

 the suitability of the photographic method of stellar 

 spectroscopy, first inaugurated by his researches, to some 

 other investigations, such as — differences which may pre- 

 sent themselves in the photographic region in the case of 

 the variable stars, the difference of relative motion of two 

 stars in the line of sight, the sun's rotation from photo- 

 graphic spectra of opposite limbs, and the spectra of the 

 different parts of a sun-spot. 



In the hope of throwing light on many physical ques- 

 tions suggested by the stellar photographs, the author has 

 taken for comparison a number of terrestrial spectra, 

 especially of hydrogen and calcium, under different 

 physical conditions. As he is still pursuing this inquiry, 

 he reserves an account of this part of his work. 



