Nov. 28, 1889] 



NATURE 



&i 



Todhunter ; but to make it effective our teachers must be 

 possessed of ordinary common- sense. So long as this is ab- 

 sent, all the elaborate and scieniifically improved editions of 

 Euclid's " Elements " in the world will not produce the much-to- 

 be-desired change. Let the teacher go through any edition of the 

 first book of Euclid's "Elements" in a common-sense manner 

 with his pupils, and he will find that, instead of the apathy and 

 general disgust exhibited by them when undergoing the ordinary 

 process of Euclidian cram, there will be a general air of bright- 

 ness, interest, and intelligent appreciation. H. 

 _ The Yorkshire College, Leeds, November 25. 



A Brilliant Meteor. 



While at my observatory to-night, at 9.37 p.m., I saw the 

 largest and brightest meteor I have seen since November 1880. 

 It became visible near v Eridani, and disappeared near a 

 Leporis. The colour was a bright greenish blue, and the 

 brightness wa-; twice or three times Venus at greatest brilliancy. 

 It cast a distinct shadow. J. COCKBURN. 



St. Boswells, N.B., November 23. 



STAR DISTANCES} 



'T'HE festal offering contributed by Prof. Oudemans to 

 -■; the Pulkowa celebration is an especially appro- 

 priate one. The incidents of the long parallax-campaign 

 can scarcely be recapitulated without recalling, in con- 

 nection with the name of F"riedrich Struve, the quorum 

 pars tnas:nnftn of yEneas. He it was who, in Sir John 

 Herschel's opinion (Memoirs R. Astronomical Society, 

 vol. xii. p. 442), made the first real impression upon the 

 problem by showing that not one of twenty-seven circum- 

 polar stars discussed in 1819-21 could possibly have an 

 annual parallax amounting to half a second of arc. 

 Thenceforward, astronomers knew what they had to 

 expect. Sanguine hopes of meeting comfortably large, 

 and properly periodical residuals among ordinary obser- 

 vations, were checked, if not extinguished. The changes 

 of stellar position reproducing, according to the laws of 

 perspective, the movement of the earth in its orbit, were 

 perceived to be on a scale so minute that their satisfactory 

 disclosure lay, for the moment, beyond the range of 

 what was feasible. Success in the enterprise, it was 

 evident, was conditional upon the employment of more 

 perfect instruments than had heretofore been available 

 with a precision and vigilance of which the very idea 

 was absent from all but a few prescient minds. Sir 

 William Herschel seemed to have anticipated the con- 

 juncture when he declared in 1782 the case to be " by no 

 means desperate," although stellar parallax should fall 

 short of a single second {Phil. Trans., vol. Ixxii. p. 83). 

 The memorable "triple event," by which, almost simul- 

 taneously, at the Cape, at Konigsberg, and at Pulkowa, 

 his confidence was justified, is familiar to all readers of 

 astronomical history. Its significance may be estimated 

 from Bessel's admission that, until the yearly oscillations 

 of 61 Cygni emerged from his measures in 1838, he was 

 completely in the dark as to whether stellar parallax was 

 to be reckoned by tenths or by thousandths of a second 

 {Astr. Nach., No. 385). 



The value to students of Prof Oudemans' synoptical 

 view of what has since then been achieved in this 

 direction can hardly be overstated. Not only does he 

 record every individual result worth considering, but 

 the tabulated particulars enable a fair judgment to be 

 formed as to the value of each. There are, indeed, one 

 or two cases in which a note of warning might with 

 advantage have been added. Thus, Dr. Brunnow's small 



'' Uebersicht der in den letzten 60 Jahren ausgefiihrten Bestimmungen 

 von Fi.\stern parallaxen." You J. A. C. Oudemans. Eine Fesigabe zum 

 Sojahrigen J.ibiiaum der Sternwarte zu Pulkowa. AstronomiscJie Nach- 

 richtcn, Nos. 2915-16. 



parallax for 85 Pegasi, to say the least, requires confir- 

 mation. A perfect equability in the mode of observing is 

 essential in such delicate operations ; but the Dunsink 

 astronomer was himself conscious of, and noted with his 

 usual care, a slight change, as the series flowed on, in his 

 habit of "bisecting" the large star {Dunsink Observa- 

 tions, vol. ii. p. 38). The distance of this interesting 

 binary system can hence scarcely be regarded as even 

 approximately known. 



Still less reliable, though for different reasons, are 

 Johnson's measures of Castor, and Captain Jacob's of o 

 Herculis. The parallax assigned to the latter star of 

 o"-o62 relative to its fifth magnitude companion cannot be 

 other than illusory, since the pair, as evidenced by a 

 small, but well-ascertained common proper motion, are 

 physically connected, and must therefore be at virtually 

 the same distance from the earth. 



Forty-nine stars, all save one measured within the 

 last sixty years, are included in Prof Oudemans' list. 

 The exception deserves particular mention. Samuel 

 Molyneux erected at his house in Kew Green in 1725, a 

 zenith sector by Graham, with which he began, in com- 

 bination with Bradley, a set of observations for parallax 

 on y Draconis. The same star had, in the previous 

 century, been similarly experimented upon by Robert 

 Hooke with something of a dubious success. The well- 

 known eventual issue of Molyneux's observations was 

 Bradley's discovery of the aberration of light ; but they 

 included besides an element of true parallactic change, 

 brought out by Dr. Auwers's discussion in 1869,^ after it 

 had lain concealed among them for 142 years The eye 

 and hand must indeed have been faithful thus to 

 record an ebb and flow of change profoundly submerged, 

 at that comparatively remote epoch, in the reigning con- 

 fusion betwen the real and the apparent places of the 

 heavenly bodies. 



A light-journey of sixty-five years (parallax = o"o5) may 

 be considered the present limit of really measurable 

 stellar distance. Forty of the forty-nine objects so 

 far investigated lie— most of them certainly, a ie\w only 

 probably— within it. Forty stars can thus be located 

 with some definiteness in space — forty among, say, forty 

 millions ! The disproportion between our knowledge on 

 the point and our ignorance is so exorbitant that general 

 conclusions seem discredited beforehand, and negative 

 ones at any rate can have no weight whatever. Never- 

 theless, one remark at least is fully warranted by the 

 evidence. 



It is this, that the largest stars are not always those 

 nearest to the earth. For to the narrow category of stars 

 at ascertained distances belong no less than seven 

 invisible to the naked eye, one of them in closer vicinity 

 to us than Sirius, all than Capella, Vega, Arcturus, or 

 Canopus. A cursory view might almost suggest— irrespective 

 of geometrical possibilities— that stellar brightness had 

 nothing whatever to do with remoteness. The legitimate 

 and certain conclusion to be derived from the facts, 

 however, is that the disparities of stellar light-power are 

 enormous. A farthing rushlight is not more insignificant 

 compared with the electric arc than a faint compared 

 with a potent sun. Sirius emits 6400 times as much light 

 as a ninth magnitude star north of Charles's Wain 

 (Argelander-Oeltzen 11,677) ; our own sun falls nearly as 

 far short of the radiative strength of Arcturus. Inequali- 

 ties of the same order between the members of revolving 

 systems emphasize this result. Sirius shines like four 

 thousand of its own companions ; and the movements of 

 other stars are perhaps swayed by almost totally obscure 

 bodies. 



The inference that the apparent lustre of individual 

 stars tells us nothing as regards their distance was already 



' Monatsberichte, Berlin, 1869. p. 630. The result places y Draconis 

 at a distance of ssi lieht-years, but with a very large "probable error" 

 (parallax = o" '092^0 070). 



