January 1, 1894.] 



KNOWLEDGE 



17 



" It would seem that this method would be about the only 

 one at all applicable to a photographic search for any planet 

 exterior to Xeptune, as the slow motion of such an object would 

 prevent its trailing on the plate, and it could not possibly be 

 distinguished from the multidudes of small stars on the photo- 

 grajjhs by ordinarj- inspection. 



" Photographs made with an interval of a few years, and 

 thus compared, would at a glance reveal dis]ilacements due to 

 proper motions of the stars — assuming that the scale suffered 

 no change in the meantime. 



■' Comparisons thus made would also readily reveal the pre 

 sence of variable stars. 



" In superposing two negatives of the same region of the 

 sky, correctly oriented to each other, very singular and interest- 

 ing systems of circles, Ac, are formed. These change their 

 positions and extent with every slight shifting of one of the 

 negatives from exact coincidence with the other." 



PHOTOGRAPHIC NEBULOSITIES IN THE MILKY WAY. 

 To the Editor of Knowledge. 



Dear Sir, — In the continuation of the photography of 

 the Milky Way, one of the plates having shown near its 

 edge a rather remarkable and large nebula where none had 

 been previously recorded, I decided to give a specially long 

 exposure on it, though the object fell in a blank region of 

 the Milky Way, in one of the large dark areas. With the 

 nebula in the 'middle of the plate, on October 13th, 1893, 

 an exposure of seven hours was given, from 8h. 20m. to 

 15h. 20m. standard Pacilic time. The instrument used 

 was the Willard lens, with which all the Milky Way and 

 comet photographs have been made. The aperture of 

 this instrument is six inches and the focal length thirty- 

 one inches. 



The resulting picture shows a very singular and 

 remarkable object — a straggling group of bright stars in 

 the centre of a vast nebula over 2^ in diameter. This 

 nebula, which is roughly roundish, has numerous irregular 

 vacancies and zigzag lanes in it, and seems to mingle 

 indefinitely with masses of small stars and become part of 

 them. As shown by the photograph it occupies a very 

 singular region, distantly surrounded by vast multitudes of 

 small stars. 



The group of stars itself is visible to the naked eye as a 



hazy spot, about 3° north-west of the variable « Cephei. 



The brightest star in the group is D.M. + 50° 2617, 



1 •!• e lorr rv • a = 21h. 34m. 29'8s. 



whose position for 1855-0 is « _ -„o ,„ „, 



which may also be taken to represent the place of the 

 nebula. 



The bright star near the north-west corner of the 

 unenlarged plate is a. Cephei. Five degrees south, and a 

 little west of a is shown the red star 2 2729, which is a 

 beautiful double. Preceding 2 2720 is the f3'5 magnitude 

 star D.M. -f 57° 2309. This latter star the photograph 

 shows to be surrounded by a rather unsymmetrical dense 

 circular nebulosity. The nebulosity is a little denser 

 following the star. The position of this object for 1855-0 



a. = 21h. 13m. 21-ls. 



5 = Jr 57° 58-9'. 



This was not previously known to be nebulous, though 

 the nebulosity can be seen as a hazy glow about the star 

 with the telescope. In the 36-inch the star itself is found 

 to be a very unequal double. Two nights' measures give 



for it jjgjojjgg ° 4-40" ' '^^^ smaller star is about 13^ 

 magnitude. 



I also send an enlargement which I have made of the 

 central part of this plate showing the large nebula to 

 better advantage, the magnification being about 2^ times. 

 This brings out very beautifully the singular structure of 



IS 



the sky in the region of the nebula. When viewed at a 

 distance of a few feet the effect is enhanced ; it is then 

 seen that the sky (Oi' Milky Way) is broken up into 

 numerous black cracks or crevices. Looking at these 

 peculiar features, I cannot well see how one can avoid the 

 conclusion that they are necessarily real vacancies in the 

 Milky Way, through which we look out into the blackness 

 of space, I am aware that Mr. Kanyard is opposed to 

 this view, and I would like to have his opinion of the 

 real nature of these apparent crevices in the Milky Way, 

 as shown on this particular plate. 



Among the many curious things shown on this photo- 

 graph, besides others which I have not the time to elaborate 

 on, will be seen a curious arch of small stars close 

 following the second brightest star in the nebula. About 

 3° following the nebula, and a little north, is a very 

 singular elliptical dark opening surrounding an island of 

 small stars. 



In reference to nebulous stars, I would say that a photo- 

 graph on September 17th, 1803, with three hours' exposure, 

 shows cu Orionis to be nebulous ; there is a curved spur of 

 nebulosity running from the .star north-westerly, and a 

 larger mass some 20' north of the star. A Orionis is also 

 nebulous, with the heaviest part of the nebulosity to the 

 west. These are verified with the 12-inch. 



Another picture, with a longer exposure, seems to show 

 a large elliptical nebulosity attached to and extending 

 southerly from a. Orionis. This latter, however, must be 

 verified by another and longer exposure, though the 

 nebulosity, if real, is strong enough on the present plate. 



Mount Hamilton, California, E. E. Barnard. 



November 14th, 1898. 



To the Editor of Knowledge. 



Dear Sir, — The interesting article on the solar faculse, 

 in the December number of Knowledge, prompts me to 

 send you some results of my own recent experience with 

 regard particularly to the reversals of the H and K lines 

 on the Sim's disc and in the prominences, these being in 

 some respects at variance with the conclusions of M. 

 Deslandres. 



A careful examination of all the spectrum photographs 

 I have obtained appears to show that, whilst every true 

 facula giving a continuous spectrum reverses the calcium 

 lines, other bright reversals are sometimes present, having 

 no corresponding facula?. In certain spot spectra, for 

 instance, the reversals are found to be continuous over 

 the whole of the disturbed region, very intense but single 

 over the spots, and wider with a central absorption line in 

 the neighbouring facula?. As a rule, however, the umbra 

 of a spot appears to give no calcium light. Thus, I should 

 be inclined to agree that the forms photographed with H 

 or K light by Prof. Hale, and recently also by myself, 

 would be more correctly described as " faculous gaseous 

 protuberances " than faculas, for they evidently do not 

 correspond exactly with facul*. 



Where I difler from M. Deslandres, however, is in 

 regarding both kinds of reversal as ordinary prominences 

 seen in projection upon the disc, and I think I have 

 obtained ample evidence showing that this may be 

 true only with regard to what I may call the eruptive 

 reversals having no corresponding faculie. According to 

 my experience, the ordinary faculie do not reverse the 

 hydrogen lines. If these objects were really prominences 

 one would expect to find the hydrogen line t, the com- 

 panion to H, of the same relative intensity as it is in the 

 prominences at the limb ; but I have failed as yet to find 

 any trace of this line. Furthermore, I have several times 



