December 19, 1895] 



NA TURE 



163 



associated with a relatively dark body ; and it is perhaps allow- 

 able to suppose a similar connection in the case of other variables 

 of the same class. Besides the possibility of eclipses, this 

 orbital movement may operate in two other ways to produce 

 light changes. If the companion be a dark body, there will be 

 phases depending upon its varying reflection of light from the 

 primary, but the changes of magnitude due to this cause will be 

 practically negligible. When the orbit is very eccentric, as in 

 8 Cephei, the temperature of the companion will vary very con- 

 siderably at different parts of the revolution, and Mr. Roberts 

 seems to regard its consequent changes of brightness as probably 

 the main cause of the variability. It is admitted, however, that 

 the variations of i "5 or 2 magnitudes, which are occasionally 

 met with, cannot be satisfactorily explained in this way, and it is 

 necessary to suppose an additional variation of the primary 

 itself due to disturbances at periastron. In the variables, like 

 i\ Aquilae, which show a secondary minimum, it is only necessary 

 to suppose that an eclipse also takes place. Attention is drawn 

 to two tests of this theory. First, the companion should show 

 itself spectroscopically at the quadrature following periastron ; 

 second, telescopic double stars having highly eccentric orbits 

 should exhibit fluctuations of magnitude depending upon the 

 distance between the components. It should be remembered 

 that there is as yet no evidence of luminosity of the companion 

 to 8 Cephei, but it may be that the exposures given to the 

 spectrum photographs have been insufficient to depict it. 



THE NEW MINERAL GASESy 

 A S Mr. Crookes has now published {Chemical News, August 

 -^ 23, 1895), the wave-lengths of the lines in the spectra of 

 the new mineral gases observed by him in the tubes supplied by 

 Prof Ramsay, I propose in the present paper to bring together 

 some notes I have made (some of them some time ago) on the 

 same subject. 



The researches made at Kensington in connection with the 

 new gases obtained from broggerite and other minerals has 

 consisted, to a large extent, of comparisons of the lines in their 

 spectra with lines in the spectra of the sun and stars. Preliminary 

 accounts of these comparisons have already been given, and 

 they show that the bright yellow line seen in the gas from 

 broggerite is by no means the only important one which appears. 

 Although the general distribution and intensities of the lines 

 in the gases from broggerite and cleveite sufficiently corre- 

 sponded with some of the chief " unknown lines" in the solar 

 chromosphere and some of the stars to render identity 

 probable, it was desirable to see how far the conclusion is 

 sustained by detailed investigations of the wave-lengths of the 

 various lines. 



The Yellow Line \ ^'i'j t^'f). — Immediately on receiving from 

 Prof. Ramsay, on March 28, a small bulb of the gas obtained 

 from cleveite, a provisional determination of wave-length was 

 made by Mr. Fowler and myself, in the absence of the sun, by 

 ijicrometric comparisons with the D lines of sodium, the result- 

 ing wave-length being 5876 07 on Rowland's scale. It was at 

 once apparent, therefore, that the gas line was not far removed 

 from the chromospheric Dj, the wave-length of which is given 

 by Rowland as 5875-98. 



The bulb being too much blackened by sparking to give 

 sufficient luminosity for further measurements, I set about 

 preparing some of the gas for myself by heating broggerite in 

 .vacua, in the manner I have already described. A new 

 measurement was thus secured on March 30 with a spectroscope 

 having a dense Jena glass prism of 60° ; this gave the wave- 

 length 5876-0. 



On April 5, I attempted to make a direct comparison with the 

 chromospheric line, but though the lines were shown to be 

 excessively near to each other, the observations were not regarded 

 as final. 



Prof. Ramsay having been kind enough to furnish me, on 

 May I, with a vacuum tube which showed the yellow line very 

 brilliantly, a further comparison with the chromosphere was 

 made on May 4. The observations were made by Mr. Fowler, 

 in the third order spectrum of a grating having 14,438 lines to 

 the inch, and the observing telescoije was fitted with a high 

 power micrometer eye-piece ; the dispersion was sufficient to 



1 "On the New Gases obtained from Uraninite. (Sixth Note.)" By J. 

 Norman Lockyer, C.B., F.R.S. Received at the Royal Society, September 

 JO, read November 21. 



NO. 1364, 



VOL 



53l 



easily show the difference of position of the Dg line on the east 

 and west limbs, due to the sun's rotation. Observations of the 

 chromosphere were therefore confined to the poles. 



During the short time that the tube retained its great 

 brilliancy, a faint line, a little less refrangible than the bright 

 yellow one, and making a close double with it, was readily seen ; 

 but afterwards a sudden change took place, and the lines almost 

 faded away. While the gas line was brilliant, it was found to 

 be " the least trace more refrangible than D3, about the thick- 

 ness of the line itself, which was but narrow " ( " Observatory 

 Note Book"). The sudden diminution in the brightness of the 

 lines made subsequent observations less certain, but the instru- 

 mental conditions being slightly varied, it was thought that the 

 gas line was probably less refrangible than the D3 line by about 

 the same amount that the first observation showed it to be more 

 refrangible. Giving the observations equal weight, the gas line 

 would thus appear to be probably coincident with the middle of 

 the chromospheric line, but if extra weight be given to the first 

 observation, made under much more favourable conditions, the 

 gas line would be slightly more refrangible than the middle of 

 the chromosphere line. 



Pressure of other work did not permit the continuation of the 

 comparisons. In the meantime, Runge and Paschen announced 

 (Nature, vol. Hi. p. 128) that they also had seen the yellow 

 line of the cleveite gas to be a close double, neither component 

 having exactly the same wave-length as Dj, according to Rowland. 

 They give the wave-length of the brightest comjwnent as 

 5878-883, and the distance apart of the lines as 0-323. 



This independent confirmation of the duplicity of the gas line 

 led me to carefully re-observe the D3 line in the chromosphere for 

 evidences of doubling. On June 14 observations were made by 

 Mr. Shackleton and myself of the D3 line in the 3rd and 4th 

 order spectra under favourable conditions ; " the line was seen 

 best in the 4th order, on an extension of the chromosphere or 

 prominence on the north-east limb of the sun. The Dj line 

 was seen very well, having every appearance of being double, 

 with a faint component on the red side, dimming away 

 gradually ; the line of demarcation between the components 

 was not well marked, but it was seen better in the prominence 

 than anywhere else on the limb" (" Observatory Note Book "). 

 It became clear, then, that the middle of the chromosphere 

 line, as ordinarily seen, and as taken in the comparison of May 

 4, does not represent the place of the brightest component of 

 the double line, so that exact coincidence was not to be 

 expected. 



Though the observations are not yet quite completed, the cir- 

 cumstance that the line is double in both gas and chromosphere 

 spectrum, in each the less refrangible component being the 

 fainter, taken in conjunction with the direct comparisons which 

 have been made, render it highly probable that one of the gases 

 obtained from cleveite is identical with that which produces 

 the Dg line in the spectrum of the chromosphere. 



Other observers have since succeeded in resolving the chromo- 

 spheric line. On June 20, Prof. Hale found the line to be 

 clearly double in the spectrum of a prominence, the less re- 

 frangible component being the fainter, and the distance apart 

 of the lines being measured as 0-357 tenth-metres (Ast. Nach., 

 3302). 



The doubling was noted with much less distinctness in the 

 spectrum of the chromosphere itself on June 24. Prof. Hale 

 points out that Rowland's value of the wave-length (as well as 

 that of 5875-924, determined by himself on June 19 and 20) 

 does not take account of the fact that the line is a close 

 double. 



Dr. Huggins, after some failures, observed the D3 line to be 

 double on July \o{Ast. Nach., 3302); he also notes that the 

 less refrangible component was the fainter, and that the distance 

 apart of the lines was about the same as that of the lines in the 

 gas from cleveite, according to Runge and Paschen. 



It may be added, that in addition to appearing in the chromo- 

 sphere, the D3 line has been observed as a bright line in nebuhe 

 by Dr. Copeiand, Prof. Keeler, and others ; in 3 Lyra- and 

 other bright line stars ; and as a dark line in such stars as 

 Bellatrix, by Mr. Fowler, Prof. Campbell, and Prof. Keeler. 

 In all these cases it is associated with other lines, which, as I 

 shall show presently, are associated with it in the spectra of the 

 new gases. 



The Blue Line, A 4471*8. — A provisional determination on 

 April 2 of the wave-length of a bright blue line, seen in the 

 spectrum of the gsses obtained from a sijecimen of cleveite, 



