Decembeb 1, 1896.] 



KNOWLEDGE 



275 



Jl cttcr g, 



[The Editors do not hold themselves responsible for the opinions or 



statements of correspondents.] 



« 



STAR SYSTEMS. 

 To tJie Editors of Knowledge. 

 SiBs, — Considering the great distance which must 

 separate the second-magnitude stars in the Great Bear 

 (for the parallax does not seem to be in any case consider- 

 able), it seems very improbable that they constitute a 

 system. Determinations of small proper motions are 

 always unreliable, and with none of these stars is the 

 proper motion large. But agreement, even in large proper 

 motions, i."? often found (though, of course, not quite exact) 

 in cases where the stars do not form a system. Thus the 

 proper motions of three of our first-magnitude stars are as 

 follows (I take them from the Cincinnati Catalogue) : — 



I'roper Motion. 



R A. Declination. 

 Sirius , ... .. - 037 - 1-20 



Procyon -0047 -103 



And Arcturus is not very dissimilar, viz., E.A. -0080, 

 declination — l-OS. Looking through the Cincinnati 

 Catalogue I get the following smaller stars with motions 

 very like the foregoing, all of which are much over the 

 average : — 



E.A. Declination. 



Lalande 30044 -0030 -1-39 



Lalande 301)94 ... -0 049 -1-49 



Lalande 31055 -00B2 -115 



36 Ophiuchi -0 039 - 1 IS 



Oeltz-Arg. 17415 -0069 -1-25 



W. 23h. 175 -0035 -1-21 



There is a small star near 3(j Ophiuchi whose proper 

 motion is almost identical with it. Can we suppose that 

 all of these stars, or even any considerable proportion of 

 them, belong to the same system ? The proper motion of 

 the last-named star and of 36 Ophiuchi agrees almost 

 exactly with that of Sirius, but their situations in the sky 

 are as follow : — 



E.A. Declination. 



Sirius 6h. 41m. - 16' 37' 



36 Ophiuchi 17h. 9m. -26^27' 



W. 23h. 175 23h. 12ni. -14=22' 



The three Lalande stars 30044, 30694, and 310.55 are 

 probably really nearer to each other than the stars in the 

 Great Bear. I might, perhaps, have added til Virginis to 

 the foregoing list. 



Probably a very considerable part of the apparent proper 

 motion of a star is due to the sun's motion in space. The ! 

 effect of this will be different when the stars differ in : 

 position. The apparent motion will moreover be, cetn-is 

 /Kiril'Wi, increased in the same proportion as the parallax ; 

 and of two stars which apparently aijree one may be at 

 double the distance of the other with half the parallax. 

 But until we know the motion of each star in the line of 

 sight we are further at sea. The effect of this may be 

 to render the real motion of the two stars which we are 

 comparini,' altogether different. 



Among the proper motions of many thousands of stars 

 there must be a large number of chance coincidences. It 

 is only when there is something exceptional in the proper 

 motions, or in the position of the stars which we are com- 

 paring, that we can draw any inference. Thus, I think, 

 though no satisfactory orbit has yet been determined for 

 61 Cygni, we may conclude that the pair are physically 

 connected. For the motion is exceptionally large, the 

 stars lie close together on the sphere, and it seems to be 

 ascertained that they have almost the same parallax. 

 Indeed, they seem to be ia reality so near each other that 

 their mutual attraction must seriously affect the motions 

 of both. W. H. S. MuNLK. 



A VERT EXTENDED STREAM OF SCXSPOTS. 

 To the Editors of Kxowledge. 



Sirs, — I have been much interested in the article on 

 " A Very Extended Stream of Sunspots," in the November 

 Number of Kxowi,Ei)r,E, and in the exquisite illustrations 

 accompanying it. 



Perhaps your readers may hke to know that this 

 wonderful outburst did not return when due after rotation, 

 with the exception of a very small spot in the same posi- 

 tion, or nearly so, as the " herald spot " alluded to in that 

 article, although a vast expanse of faculae, visible on the 

 eastern limb of the sun's disc, and again on the western 

 limb, testified to the dying embers of the great distirrbince. 



If I may be permitted to criticize, I should like to 

 enquire the special meaning attached in this case to the 

 term "nebulosity,'' which does not seem quite applicable 

 to the small fragmentary spots indicated, yet can hardly 

 be intended to signify the faculous hght sometimes 

 apparent even when the spots are far advanced towards 

 the centre. The word " bivalve, " on the other hand, as 

 applied to segmented spots, is singularly appropriate in 

 describing a type very distinct and of frequent occurrence. 



This stream was observed, and drawings, as well as 

 photographs, secured, by the members of the Solar Section 

 of the British Astronomical Association during eleven 

 days out of the thirteen during which it was visible. 



E. Bbowm. 



[By " nebulosity " I wished to indicate the LU-defined, 

 faint, dusky markings seen in some parts of the great group 

 in its earlier days. — E. W.\lier M\c.ndkk.] 



VARIABLE ?;TARS. 

 To the Editors of Knowledge. 



SiBs, — Since the article on the above subject, which 

 appeared in the August Number of Knowxedge, was written. 

 Dr. Chandler's "Third Catalogue of Variable Stars" has 

 been published. It may therefore be interesting to note 

 the progress recently made in this branch of astronomy, by 

 comparing this catalogue and the preceding one. The 

 total number of variable stars in the Third Catalogue is 

 three hundred and ninety-four, against three hundred and 

 forty-three in the Second, and one hundred and eighty- 

 seven in Mr. Gore's Catalogue of 1^86. Thus tifty-one 

 stars have been discovered or confirmed in the interval 

 between the Second and Third Catalogues, a noteworthy 

 addition to our knowledge in this department. In fact, if 

 we go on advancing at the same rate in the future, it is 

 very probable that the number of variables may exceed 

 the number of the known asteroids. 



'I'he comparison in the classification of the stars is as 

 follows : — 



CI. r. II. Ill IV. V. Total. 



Second Catalogue and Supplement 11 239 31 47 15 3+3 

 Deduct not confinucd ... ... — 4 — 1 — 5 



Add since discovoivd 



11 233 31 46 13 338 

 2 47 — 6 X 56 



Third Cntiiloguc ... ... . 13 282 31 52 16 394 



The classes have the same signiGcation as in the article 

 alluded to, viz. : — 



I. Temporary or new stars. 

 II. Variation of one hundred days and upwards. 



III. Irregular. 



IV. Variations of less than one hundred days. 

 V. Algol type. 



The long-period variables continue their superiority in 

 numbers, while only two new and one Algol type have 

 been added. 



As regards distribution in hemispheres, there are now 



