NOTES. 



ASTRONOMY. 



By .\. C. D. Crommehn. B..\.. D.Sc. K.K..\.S. 



.\IETKORS. — An important paper on meteors has been 

 published by Charles P. Olivier in the Traiisuctions of the 

 Aiiicrican Philosophical Society. He has discussed the 

 observations of six thousand five hundred meteors seen 

 between 1S9S and 1910, and deduced one hundred and 

 seventy-five parabolic orbits; a great many were observed 

 by himself at the Lick Observatory. He makes an absolute 

 rule that radiants nnist only be determined by combining 

 observations made on the same night, and .'^ays that neglect of 

 this rule has led to the deduction of many fictitious radiants. 

 Most of the meteors were seen in July, August, October, 

 November ; several in January, .April, .May, a few in December. 

 There were no observations in February, March, June, 

 September. 



The first shower discussed is the Aquarids. of which good 

 observations were obtained on 1910, May S"" -0, e*" -9, 12'' -0 

 G.M.T. The radiants at the three dates were: (II 334°-0 — 

 3''-4. (i)337°-7-0°-6, (3) 34i-0-0°-6. The parabolic orbits, 

 and the orbit of Halley's comet, are given below, also the 

 orbit of the Orionids (4). 



The connection of the meteors with the comet is considered 

 established, but they have spread out greatly from the comet's 

 orbit. In fact, a cylinder of radius thirteen million miles 

 appears to be tilled with them. It seems not impossible that 

 the Orionid Stream may also have a connection with the 

 comet, meeting the Earth near the other node of the orbit. 

 The connection, however, is far more doubtful than in the 

 case of the Aquarids. The Perseids and the October streams 

 are fully discussed, the latter being shown to consist of amain 

 stream and a number of minor ones, with radiants separated 

 by sever.il degrees. It is suggested that these minor streams 

 had the same origin as the great stream, but have been 

 gradually separated from it. He does not accept the stationary 

 position of the Orionid radiant, but finds evidence of an east- 

 ward motion. He doubts the reality of stationary radiants in 

 other cases also, and follows Bredichin in the view that they 

 arc composite. Of the one hundred and seventy-five orbits 

 only twenty-seven are direct, but this arises from the greater 

 chance of our meeting a meteor moving in the reverse direction 

 to the Earth, just as more trams pass a pedestrian in the 

 opposite direction to his motion. Twenty-eight perihelia lie 

 in the first quadrant of longitude, sixty-six in the second, sixteen 

 in the third, fifty-five in the fourth. 



He notes as evidence of the clearness of the atmosphere 

 at Mt. Hamilton that most of the meteors seen there are of 

 the fourth magnitude, while in \'irginia those of the third 

 magnitude predominated. Yellow meteors have the shortest 

 time of visibility, red and orange longer, green and white 

 longest. 



GROUPS OF STARS WITH COMMON DRIFT.— 

 Several groups of stars that seem to be travelling in company 

 have now- been recognised. The best known is the Ursa 

 Major group, to which Sirius was recently added. There is a 

 group in Taurus, and one in Perseus. Mr. Benjamin Boss 

 ^Astron. Jouni. No. 629) makes a notable addition to the 

 list, having detected a group of stars with large proper motions, 



which appear to be moving with equal velocities on nearly 

 parallel lines. The following is the list of stars. Their con- 

 \ergcnt point is R-.A. 6'' 37"', N. Dec. 0-5. The observed and 

 computed position angles of the motion of each are given ; it 

 will be seen how closely they agree, /» is the Proper Motion 

 in a century. 



To test the matter further, Mr. Boss examined the radial 

 motions, as far as these are available. The linear velocity of 

 the group relatively to the Sun is ninety-five kilometres per 

 second. With the exception of the second star (which 

 possibly does not belong to the group) the results are 

 surprisingly harmonious, and leave no doubt of the reality 

 of the common drift. 



The computed and observed parallaxes are also compared. 

 In several cases there is good accordance ; in the case of the 

 smaller parallaxes the observed values are uncertain. The 

 stars are in the same order as in the first list. 



I have already alluded to Mr. Eddington's paper on "Star 

 distribution" at the British .Association. One interesting 

 point that he brings out is that the actual frequency of stars 

 of different spectral types may be very different from their 

 frequency in our catalogues. Thus, in his list of the seven- 

 teen newest stars three arc of the type denoted by Ma. while in 

 our catalogues only one star in fifteen is of this type. 



The Orion or Helium tvpe (denoted by ji) is commoner in 

 the catalogue than Ma, but none appear among our nearest 

 neighbours. He gives as the explanation that Ma stars are 

 really pretty common everywhere, but, being intrinsically very 

 faint, cannot be seen at great distances ; while the Helium 

 stars are very rare, but being of extreme brilliance are visible 

 at immense distances. This is confirmed by the failure to 

 detect sensible parallax in such stars. 



