148 



KNOWLEDGE 



[August 1, 1893. 



aud variables of short or long periods. This general 

 statement of their absence, however, since it rests upon 

 purely negative evidence, may need more and more quali- 

 fication with the advance of photographic research. 

 Nate hij the EiUtvr. 



[Everyone will admit the extremely interesting nature 

 of the questions discussed in Miss Gierke's paper, and 

 though we may not all agree with her in the very definite 

 conclusions she draws as to the existence of stratified 

 layers of absorbing vapour about the sun and stars, and 

 as to their relative positions and temperatures, the mere 

 discussion of such questions is likely to be instructive. I 

 wish, however, to guard myself, as Editor, from being 

 supposed to put forward her views as generally received. 



Personally I am disposed to doubt the existence of the 

 shallow layer of cool vapour above the photosphere which 

 Miss Gierke, as well as other writers, have assumed to 

 exist in order to account for the dark lines of the 

 Fraunhofer spectrum. Nearly all the lines of the Fraun- 

 hofer spectrum, whether they are broad or thin, hazy or 

 dark, do not change in breadth and intensity in passing 

 from the centre of the sun's disc to the solar limb ; 

 whereas with a shallow absorbing layer, we should expect 

 to find much greater absorption near the limb, where the 

 distance of transit obliquely through a shallow stratum 

 and the consequent absorption would produce a greater 

 blackness of the lines than at the centre of the solar disc, 

 where the light has only to pass through the vertical 

 thickness of the stratum. 



Prof. Hale's photographs, as well as direct observations, 

 prove that in the region of the facuLne the H aud K lines 

 are very bright compared with the light of other wave- 

 lengths emanating from the sun's disc. If the vapour 

 which absorbs the Fraunhofer Unas extends to a great 

 height above the faculfe, we should expect it to reduce 

 the light of the faculse as well as the light of the photo- 

 sphere. To take a simple example, let us suppose that it 

 halves the brightness of light of K wave-length and reduces 

 the light of the continuous spectrum of the photosphere so 

 that a line is produced in the K region which appears rela- 

 tively dark compared with the continuous spectrum on 

 either side of it. But the K light from the facula' may be 

 so bright that after half its brightness is absorbed it still 

 appears bright compared with the continuous spectrum 

 on either side of it. It will be noticed that it is only the 

 brighter central part of the K line that gets through and 

 appears bright as compared with the spectrum on either 

 side of it ; the fainter wings of the bright line are so 

 reduced as to be lost, and at a very little distance they are 

 reversed so that the central part appears bright in the midst 

 of a nebulous dark band — the intensity of absorption 

 evidently to some extent depends on the difference of 

 temperature of the emitting and absorbing medium — and 

 it seems probable that the proportion of light absorbed 

 from the hot photosphere would be greater than the propor- 

 tion absorbed from the cooler incandescent gas above the 

 photosphere. The absence of the H line in the Mira 

 spectrum cannot be taken as proving that the cool 

 calcium-vapour is above the glowing hydrogen. The 

 absorbing calcium-vapour may be in the same region, and 

 mtermixed with the glowing hydrogen. It is only necessary 

 to suppose that hydrogen glows with H light at a lower 

 temperature than calcium-vapour, and that each foot in 

 depth of calcium-vapour absorbs the H radiations emitted 

 by the preceding foot of hot hydrogen. 



The many vertical eruptions in the chromosphere and 

 corona, as weU. as what we know of the law of gaseous 

 diffusion, seem to render it improbable that there is any 

 horizontal stratification of gases into thin layers upon the 



sun, and to lead to the conclusion that the appearance of 

 stratification presented by the lower regions of the chromo- 

 sphere and by the even surface of the jjhotosphere is due 

 to the difl'erence of temperature at different levels, the 

 isothermal surfaces about the heated nucleus of the sun 

 being a series of concentric spheres. — A. C. Ranyard.] 



Mr. M. Glover, of 124, Stephen's Green, Dublin, writes, 

 enclosing two photographs of a mock sun which he 

 observed at Dublin on the evening of the 30tli of -lune last. 

 The phenomenon was first noticed about 7.30 p.m., and 

 remained visible for about twenty minutes. The photo- 

 graphs were made with very short exposures, and show the 

 sun's disc seen through cirro-stratus cloud, with a spurious 

 image of the sun also seen through cloud at a distance of 

 about 2.5° from the sun, and at about the same altitude above 

 the horizon. A similar image was seen by Mr. Glover on 

 the left hand of the sun, but it had faded away before the 

 photographs were taken. 



Prof. W. Vf. Payne, of Carleton College, Northfield, 

 Minnesota, is about to issue a new astronomical magazine, 

 to be entitled Pojinhn- Astninonn/. It will be issued 

 monthly, except in .July and August, and is intended to 

 meet the wants of "amateurs, teachers, students of 

 astronomy aud popular readers." 



Scientific investigators are beginning to consider very 

 seriously the problem of a too rapidly acciniiulating 

 literature. The essence of scientific research is the 

 marshalling and comparison of facts, but as each of the 

 multiplying class of investigators brings in his contribu- 

 tion the need is felt of some authoritative organization of 

 these units into a larger body of knowledge. Scientific 

 publications overlap excessively and there is no reliable 

 index, so that unless a specialist is so happily situated as to 

 see all of the great number of periodicals which may 

 contain work affecting him, he goes in constant danger and 

 dread of missing what may be of vital importance to his 

 own enquiries. Even if he has access to all the literature, 

 the time he will have free for original work is considerably 

 diminished by his study of the work of other men, and by 

 his searches through the chaos of published papers. So 

 much is this the case that it would not be hard to point to 

 men who are not so much scientific enquirers as scientific 

 scholars, devoted almost entirely to keeping pace with the 

 infinite ramification of current work. A clearer definition 

 of the province of certain scientific magazines may possibly 

 do a little to diminish the difiiculty, but the trouble will 

 only be fully met by the establishment of subject indices. 

 One of our contemporaries, which is always ready to 

 advocate any scheme for getting money from the Govern- 

 ment, urges that a general subject Index of Science should 

 be established on a generous scale. It seems to us that 

 the red tape methods of officialism are not suitable for 

 such an undertaking, and that the work would be more 

 satisfactorily accomplished if each of the learned societies 

 would publish annually or quarterly a full subject index in 

 its own department ; and that the best results would be 

 obtained if each specialist could be induced to give with 

 each book and paper issued full references to the 

 authorities he has used. 



Local telegrams are now transmitted through pneumatic 



tubes in most of the principal cities of Great Britain. At 



present about .50 miles of such tubes are in operation, 



' requiring an aggregate of 100 horse-power and transmitting 



I a daily average of 10.5,01)0 messages, or 30 millions 



j annually. More than half of these are in London. 



