254 



SCIENCE, 



[Vol. XVIIl. No. 457 



the absolute longitude of the solar apex from observations of 

 tlie eclipses of Jupiter's satellites (Proc. Eoy. Soc, vol. xxx. 

 p. 109). But this is far from likely. 



In the first place, the revolutions of the Jovian system 

 cannot be predicted with anything like the required ac- 

 curacy. In the second place, there is no certainty that the 

 postulated phenomena have any real existence. If, however, 

 it be safe to assume that the solar system, cutting its way 

 through space, virtually raises an ethereal counter-current, 

 and if it be further granted that light travels faster with 

 than against such a current, then indeed it becomes specula- 

 tively possible, through slight alternate accelerations and re- 

 tardations of eclipses taking place respectively ahead of and 

 in the wake of the sun, to determine his absolute path in space 

 as projected upon the ecliptic. That is to say, the longitude 

 of the apex could be deduced together with the resolved part 

 of the solar velocity; the latitude of the apex, as well as the 

 component of velocity perpendicular to the plane of the 

 ecliptic, remaining, however, unknown. 



The beaten track, meanwhile, has conducted two recent 

 inquiries to results of some interest. The chief aim of each 

 was the detection of systematic peculiarities in tlie motions 

 of stellar assemblages after the subtraction from them of 

 their common perspective element. By varying the mate- 

 rials and method of analysis, Professor Lewis Boss, director 

 of the Albany Observatory, hopes that corresponding varia- 

 tions in the upshot may betray a significant character. Thus, 

 if stars selected on different principles give notably and con- 

 sistently different results, the cause of the difference may 

 with some show of reason be supposed to reside in specialities 

 of movement appertaining to the several groups. Professor 

 Boss broke ground in this direction by investigating 284 

 proper motions, few of which had been similarly employed 

 before (Astr. Jour., No. 213). They were all taken from an 

 equatorial zone 4" 20' in breadth, with a mean declination 

 of -|-3''', observed at Albany for the catalogue of the Astro- 

 Momische Gesellschaft, and furnished data accordingly for a 

 virtually independent research of a somewhat distinctive 

 kind. It was carried out to three separate conclusions. Set- 

 ting aside five stars with secular movements ranging above 

 100", Professor Boss divided the 279 left available into two 

 sets — one of 135 stars brighter, the other of 144 stars fainter, 

 than the eighth magnitude. The first collection gave for 

 the goal of solar translation a point about 4° north of a 

 Lyra, in R. A. 280°, Decl. -|-43°; the second, one some 

 thirty-seven minutes of time to the west of d Cygui, in E.A. 

 286'^, Decl. -|- 45°. For a third and final solution, twenty- 

 six stars moving 40"-100" were rejected, and the remaining 

 253 classed in a single series. The upshot of their discussion 

 was to shift the apex of movement to R. A. 289"^, Decl. -|- 51°. 

 So far as the difference from the previous pair of results is 

 capable of interpretation, it would seem to imply a predomi- 

 nant set towards the north-east of the twenty-six swifter 

 motions subsequently dismissed as prejudicial, but in truth 

 the daita employed were not accurate enough to warrant so 

 definite an inference. The Albany proper motions, as Pro 

 ffessor Boss was careful to explain, depend for the most part 

 upon the right ascensions of Bessel's and Lalande's zones, 

 and are hence subject to large errors. Their study must be 

 regarded as suggestive ratiiei than decisive. 



A better quality and a larger quantity of material was dis- 

 posed of by the latest and perhaps the most laborious inves- 

 tigator of this intricate problem. M. Oscar Stumpe of Bonn 

 (Astr. Nach., Nos. 2999, 3000) took his stars, to the number 

 of 1,054, from various quarters, if chiefly from .\uwers's and 



Argelander's lists, critically testing, however, the movement 

 attributed to ea^.-h of not less than 16" a century. This he 

 fixed as the limit of secure determination, unless for stars 

 observed with exceptional constancy and care. His discus- 

 sion of them is instructive in more ways than one. Adopt- 

 ing (the additional couiputative burden imposed by it not- 

 withstanding) Schonfeld's modification of Airy's formulae, 

 he introduced into his equations a fifth unknown quantity 

 expressivu of a possible stellar drift in galactic longitude. A 

 negative result was obtained. No symptom came to light of 

 " rotation " in the plane of the Milky Way. 



M. Stumpe's intrepid industry was further shown in his 

 disregard of customary "scamping "subterfuges. Expedients 

 for abbreviation vainly spread their allurements; every one 

 of his 2,108 equations was separately and resolutely solved. 

 A more important innovation was his substitution of proper 

 motion for magnitude as a criterion of remoteness. Dividing 

 his stars on this principle into four groups, he obtained an 

 apex for the sun's translation corresponding to each as fol- 

 lows : — 



Group. Number of Proper motion. Apex. 



included stars. . . o o 



I. 551 0.16 to 0.32 R.A. 287.4 Decl. + 42 



IL 340 0.32 to 0.64 " 279.7 " 40.5 



III. 105 0.64 to 1.28 " 287.9 " 32.1 



IV. 58 1 28 and upwards " 285.2 " 30.4 

 Here, again, we find a marked and progressive descent of 



the apex towards the equator with the increasing swiftness 

 of the objects serving for its determination, leading to the 

 suspicion that the most northerly may be the most genuine 

 position, because the one least affected by stellar individuali- 

 ties of movement. By nearly all recent investigations, more- 

 over, the solar point de mire has been placed considerably 

 further to the east and nearer to the Milky Way than seemed 

 admissible to their predecessors, so that the constellation 

 Lyra may now be said to have a stronger claim than Her- 

 cules to include it; and the necessity has almost disappeared 

 for attribuiing to the solar orbit a high inclination to the 

 medial galactic plane. 



From both the Albany and the Bonn discussions, there 

 emerged with singular clearness a highly significant relation. 

 The mean magnitudes of the two groups into which Pro- 

 fessor Boss divided his 279 stars, were respectively 6.6 and 

 8.6, the corresponding mean proper motions 21.9" and 20.9". 

 In other words, a set of stars on the whole six times brighter 

 than another set owned a scarcely larger sum-total of appar- 

 ent displacement. And that this approximate equality of 

 movement really denoted approximate equality of mean dis- 

 tance was made manifest by the further circumstance that 

 the secular journey of the sun proved to subtend nearly the 

 same angle whichever of the groups was made the stand- 

 point for its survey. Indeed, the fainter collection actually 

 gave the larger angle (13.73" as against 12.39"), and so far 

 an indication that the stars composing it were, on an aver- 

 age, nearer to the earth than the much brighter ones consid- 

 ered apart. 



A result similar in character was reached by M. Stumpe. 

 Between the mobility of his star groups and the values de- 

 rived from them for the angular movement of the sun the 

 conformity proved so close as materially to strengthen the 

 inference that apparent movement measures real distance. 

 The mean brilliancy of his classified stars seemed, on the 

 contrary, quite independent of their mobility. Indeed, its 

 changes tended in an opposite direction. The mean magni- 

 tude of the slowest group was 6.0, of the swiftest 6.5, of the 



