June 1, 1898.] 



KNOWLEDGE. 



113 



magnitude lie between us and the ring, and that a con- 

 siderable ntimber of the brighter Sirian stars do so. As far 

 as the solar stars are concerned, this conclusion falls in 

 ■with Prof. Pickering's. 



I do not think Prof. Kapteyn assumes that proper motion 

 is to be regarded as a measure of the distance of a star. 

 He considers it established (and I made a similar remark) 

 by the fact that stars with large proper motion afford as 

 striking evidence of the motion of the solar system in 

 space as stars with small proper motion ; to which it may 

 be added, that spectroscopic observations do not show that 

 stars with large proper motion have a greater average 

 velocity in the line of sight. Undoubtedly, however, 

 further observation is necessary before we can say 

 positively that the solar stars are or are not (on the 

 average) moving with greater absolute velocity than the 

 Sirian. Sirian stars with considerable proper motion are 

 not numerous, while the measurement of small proper 

 motions involves great uncertainty. But to the objection 

 that a fast-moving group of solar stars could not exist as a 

 system there are many answers. First, Prof. Kapteyn 

 seems to be of opinion that their motion is only apparently 

 and not really faster than elsewhere. Secondly, he thinks 

 it at least possible that the proportion of solar stars is 

 equally great at greater distances, the faintness of remote 

 solar stars being the only reason why this fact has not been 

 recognized. (I have, I think, also suggested both of these 

 points.) Thirdly, it does not follow that what may now 

 be regarded as a cluster forms a permanent and stable 

 system ; and lastly, the apparently rapid motion of this 

 cluster may arise (at least in part) from the sun being a 

 runaway star, as 1830 Groombridge is supposed to be. 



Prof. Kapteyn does not seem to have drawn the dis- 

 tinction between Capellan and Arcturian stars, which I 

 think will prove to be of almost equal importance with 

 that between Sirian and solar. The cluster round the 

 sun (if it be really a cluster and not merely an average 

 specimen of what is to be met with throughout space) 

 seems to be pre-eminently a cluster of Capellan stars. 



Truly yours, 



W. H. S. MoNCK. 



[I was mistaken in saying that Mr. Marth's Catalogue 

 of Milky Way Stars did not include all stars down to the 

 sixth magnitude. His original catalogue did not, but his 

 recent catalogue includes all stars in the neighbourhood of 

 the Milky Way down to the sixth magnitude of the Harvard 

 Photometric Catalogue. 



Many of the stars with swift proper motions are moving 

 athwart the direction of the sun's motion in space, and 

 the apparent motions of some of them are more or less 

 parallel to and in the same direction as the sun's motion. 

 These motions cannot be accounted for as only apparent 

 and due to the sun's motion. We may, therefore, assert 

 with some certainty that such swift-moving stars cannot 

 be, as it were, anchored in space, controlled by the gravity 

 of a cluster of a few hundred stars similar in mass to our 

 sun. — A. C. Ranyard.1 



THE 1) ARGUS RKGION OF THE MILKY WAY. 

 To the Editor of Knowledgk. 



Sir, — Few regions in the heavens can equal this in 

 interest when we consider the remarkable changes in the 

 variability of the principal star and the appearances of the 

 star-cluster and nebula surrounding it ; to use Miss Gierke's 

 expression, " the crowd of small stars embroidering one of 

 the finest of the southern nebul*." Photography now 

 enables some of those who have not had the advantage of 

 seeing this glorious object directly to examine it in the 



plates which Dr. Gill has brought over from the Cape ; 

 and all readers of Knowlkdgf, must appreciate the repro- 

 ductions you have placed within their reach of these and 

 Mr. Russell's photographs taken at Sydney. 



I beg to offer you a few remarks on the history of 

 the region, supplementary to those you have given. It 

 does not appear that Halley, when he observed the star, 

 noticed the nebulous matter adjacent to it, for it is not 

 included in the list (only six in number) of nebulse given 

 by him in the Philnndphicul Tranxdctioiin for 1716. So far 

 as I am aware, Lacaille was the first to observe the nebula, 

 which he describes in the Mrntoii-cs dc V Academic dcs Sciences 

 for 1755. He gives three lists of star-clusters and nebulffi 

 in the southern hemisphere, the third of which consists of 

 " etoiles accompagnees de nebulosite." Of these, tj Argiis 

 is the sixth, thus described : — " Gros groupe d'un grand 

 nombre de petites etoiles pen serrees, et remplissant 

 I'espace d'une espece de demi-cercle de 15 a 20 minutes de 

 diametre, avec une legere nebulosite repandue dans cet 

 espace." After LacaiUe, Dunlop appears to have been the 

 first to observe this nebula, which he describes and figures 

 in his catalogue of nebulie and clusters formed from obser- 

 vations made at Paramatta in 1826-7, and published in 

 the PhihtsopJiind Transactions, for 1828. i; Argus is number 

 309 in his list, and he describes it as " a bright star of the 

 third magnitude, suiTounded by a multitude of small stars 

 and pretty strong nebulosity, very similar in its nature to 

 that in Orion, but not so bright. . . . The nebulosity is 

 pretty strongly marked ; that on the south side is very 

 unequal in brightness, and the different portions of the 

 nebulosity are completely detached, as represented in the 

 figure. There is much nebulosity in this place, and very 

 much extensive nebulosity throughout the Robur Caroli, 

 which is also very rich in small stars." Not many years 

 after Dunlop's observations Sir John Herschel made his 

 famous astronomical expedition to the Gape. It is well 

 known that he found that some of the objects set down as 

 nebulae by Dunlop had no real existence, the cause which 

 misled him being probably want of sufficient light or 

 defining power in his instrument. But to this I need not 

 further allude. Those who have not access to Herschel's 

 work on the results of his Cape observations will be grateful 

 to you for the reproduction in Knowledge of his drawing 

 of the grand nebula in t) Argiis, now so beautifully brought 

 before us in the photographs. But I scarcely think you 

 will agree with Herschel in considering it probable that 

 the nebulous matter is far beyond the stellar cluster, which 

 forms a part of the Milky Way, for, apart from al) other 

 considerations, on that view how appallingly enormous 

 would be its extent ! May I ask whether the spectroscope 

 has ever been applied to this region ? 



Yours faithfully, 



Blackheath, May 12th, 189D. W. T. Lynn. 



PHOSPHORESCENT METEORS. 

 To the Editor of Knowledge. 



Dear Sir, — Some twenty years ago I had an experience 

 similar to that recorded from Thurso, in Prof. Tomlinson's 

 paper in Knowledge. 



I was staying the night with a friend. We sat up late, 

 and when he had gone down to see that the house was 

 safe, he returned rather promptly with the news that there 

 was someone in the pantry, for he could see a light. 

 Arming ourselves with the fire-irons, we crept downstairs. 



The pantry was between the basement passage and the 

 scullery, without external ventilation. As we turned 

 towards the wire gauze door, the light was plain enough, 

 rather bigger than a large open hand. 



