December, 1913. 



KNOWLEDGE. 



461 



He does not recommend this method except for stars of types 

 A and B (Sirius and Orion). In solar and red stars the 

 artificial line is confused with stellar lines. 



He gives a third method, but as he considers it less hopeful 

 I do not describe it. 



In the case of object-glasses too large to cover by objective 

 prisms, he suggests the use of an auxiliary lens, placed in 

 the cone of rays from the objective, so as to give a smaller 

 pencil of parallel light than that falling on the objective. In 

 this way a smaller prism will suffice, without sacrificing any of 

 the aperture. 



It goes without saying that a less degree of accuracy is 

 expected than with the slit method. But what is desired is 

 not so much the exact motion of individual stars as averages 

 for large groups of stars of different types, 

 and distributed over the sky. For this 

 purpose the new methods are full of promise. 



c* 



*. 



• a 



COMETS. — In recent years, the autumn 

 has been the great time for comets, and this 

 year has been no exception ; four comets, 

 three of them periodic, have been under 

 observation. Westphal's is the most impor- 

 tant, from its association with Neptune. It 

 presented an interesting appearance early in 

 October, being easily visible in an opera 

 glass (so that Mrs. F. Wilson found it 

 without knowing of its previous discovery) 

 and having been glimpsed with the unaided 

 eye. However, it did not live up to this 

 early promise. It grew faint and diffused, in 

 spite of its approach to the Sun, and by the 

 end of October was very difficult to see. 



On October 22nd it passed within half a 

 degree of Metcalf's comet, and the unusual 

 spectacle was afforded of two comets in the 

 same field. Both were then of the ninth mag- 

 nitude. As Westphal's is not at perihelion till 3 p.m. on 

 November 26th, it is quite likely that there may be another 

 outburst of activity. This uncertainty about the physical 

 behaviour of comets adds interest to their study. During 

 December Westphal's will be about 40' south of the ephemeris 

 given last month ; the R.A. will be a minute or more in excess 

 of the ephemeris. Corrected elements by Miss Levy : 

 Omega 56° 31' 36", Node 346° 47' 45", inclination 42° 33' 7", 

 Period 61-121 years, Log. q. 0-1012, Log. a. 1-1908. 



Neujmin's comet was interesting in two ways ; first for its 

 appearance. It was exactly like a small star with a faint 

 nebulous appendage to the south-east. This stellar appear- 

 ance enabled its position to be fixed with great accuracy. 

 Herr Stracke has computed the following orbit. Perihelion, 

 1913, Aug. 16-31 Berlin, Omega 346° 7' 52", Node 357° 54' 19" 

 inclination 14° 52' 34", eccentricity -7786, Period 18-16 years ; 

 perihelion distance 1-5300, aphelion distance 12-288. 



The comet appears to belong to the group that owns 

 allegiance to Saturn. Two other members of the group are 

 known. One is Tuttle's comet, the other was discovered by 

 Peters in 1846, but has never been seen since. It is to be 

 hoped that the period of the present comet will be accurately 

 determined, to facilitate its recovery at its next return. 



A comet discovered by Dr. Zinner at Bamberg, 1913 e, is 

 identical with Giacobini's comet, 1900, III, the period being 

 6-465 years. Perihelion passage is 1913, November 2-30, 

 Omega 171° 32', Node 193° 0', inclination 32° 17' log. q. 9-9961. 

 Owing to its rapid southerly motion it will soon be out of 

 reach of European observers. 



THE ANDROMEDA NEBULA.— Lowell Bulletin No. 58, 

 contains an investigation by Mr. V. M. Slipher on the radial 

 velocity of this nebula. It has been known for some years 

 that there were some Fraunhofer lines in its faint continuous 

 spectrum. He secured four plates last autumn and winter 

 with exposures of about seven hours each, and obtains the 

 startling result that the nebula is approaching us at the rate 

 of 297 kilometres per second, the individual values being 284, 

 296, 308, 301. It is a little difficult to credit that such a vast 



Figure 537. 

 Neujmin's Comet as sketched by 

 Prof. Barnard. 1913, Sept. 9th. 



Star a is Nicolaiev 5064, mag. 8.3 ; 



b is of mag. 11.7 ; c, 11.4 ; comet, 



11.5. The distance a-c is 4|*, 



South is at the top. 



object as this nebula (certainly several light-years in length) 

 can be moving bodily with such inconceivable speed, and the 

 results will doubtless be discussed by skilled spectroscopists, 

 to see if there is any other explanation of the shifts of the 

 lines. Mr. Slipher notes that the shift in the violet was twice 

 that in the blue, which accords with the supposition that it is 

 due to velocity. If it really has a speed of this order, its 

 distance must be very great, or it would have a sensible 

 proper motion ; for the direction of motion is not likely to be 

 exactly radial. 



I have lately been examining the photographs of this nebula, 

 and it appears to me that there are far more cases where 

 curves of stars mark out and follow the shape of 

 prominent portions of the nebula than we can reasonably 

 attribute to chance. In my view these 

 stars are actually associated with the nebula. 

 If this assumption is true it is of twofold 

 importance ; first, it would dispose of the 

 theory that the nebula is an external galaxy, 

 for these stars are exactly like those forming 

 the background of the sky in ordinary 

 regions, and obviously belonging to our 

 galaxy. Secondly, these stars could be 

 examined for parallax and proper motion 

 much more easily than the nebula itself, 

 since its outlines are vague. The case of 

 the Orion nebula may be recalled ; Sir W. 

 Huggins considered it established that the 

 stars forming the Trapezium were actually, 

 not merely optically, associated with the 

 nebula, so that they could be examined for 

 parallax and proper motion, instead of the 

 nebula itself; the soundness of this view is 

 generally admitted. 



.y>,'.';.:-':?;5>i 



JSStt 



CAMPBELL'S "STELLAR MOTIONS," 

 AND SIR DAVID GILL'S "HISTORY 

 OF THE CAPE OB S E RVATO RY."— These two 

 books have lately appeared. The first, which is the 

 " Silliman Lectures, 1910" should be read by all who 

 desire an intimate acquaintance with the marvellous precision 

 of modern spectrographic work, especially as applied to 

 motion in the line of sight, and the countless precautions 

 that are taken to avoid systematic errors in the results. In 

 our own system the method has been applied to various 

 problems : the rotation of the Sun, Venus, and Uranus, and 

 the optical verification of the fact that Saturn's ring is com- 

 posed of small particles with independent motion. In the 

 stellar heavens the method has given a new determination of 

 the direction and speed of the Sun's motion ; it has given 

 great help in forming estimates of the distances of various 

 classes of stars, and in demonstrating the unexpected fact 

 that the speed of a star increases as its spectral type advances. 

 Its application to the study of Algol variables and those of the 

 Beta Lyrae, Cepheid and Geminid types, are also dealt with, 

 and some interesting conclusions are drawn from statistics of 

 spectroscopic doubles. 



Sir David Gill gives a resume of the important problems 

 with which the Cape Observatory has been associated. The 

 distances of the Sun, Moon, and Stars, Jupiter's satellites, The 

 Cape Photographic Durchmusterung, double stars, spectro- 

 scopic work, the survey of Africa, are all dealt with. I hope 

 to give some further notes on this book in a future month, but 

 in the meantime I recommend our readers to study it for 

 themselves. 



DISTRIBUTION OF CLUSTERS AND NEBULAE.— 

 Dr. Charlier, of Lund, has published some statistics in tabular 

 and graphical form of the distribution of clusters and nebulae 

 in various regions of the sky : they are based on the three 

 catalogues of Dreyer, containing 13,223 objects, of which 769 

 are clusters. The clusters show an unmistakable tendency 

 to congregate along, or near, the Milky Way. This seems to 

 show that most of the clusters are actually involved in the 

 star-clouds of the Milky Way, and are consequently extremely 

 distant. The individual stars may therefore be very much 



