XOTliS. 



ASTRONOMY. 



Hy A. C. 1). Ckommelin, H.A.. U.Sc. F.K.A.S. 



I BEGIN my notes by expressing my sense of the loss that 

 Astronomy h.is sustained in the death of Nfr. W. T. Lynn. 

 His name has become well-known throughout the astro- 

 nomical world for his laborious researches connected with 

 the biographies of astronomers and the clearing up of obscure 

 points in astronomical history. His little books on Comets 

 and Eclipses did much to spread a knowledge on 

 these points, and their popularity is shown by the 

 frequent new editions that were called for. His 

 birth appropriately coincided with the appearance of 

 Halley's Comet in 18j5. so that his life was 

 practically coeval with a revolution of the comet. 



He worked to the last, having read a paper before 

 the British .\stronomical .\ssociation in November, 

 and contributed letters to the recent and forth 

 coming numbers of the Obsenuitory. 



AKK THE WHITE XEBLLAE GALA.XIES- 

 — If one opens an astronomical text-book of some 

 sixty years .a.go one will probably find it supporting 

 the view that the nebulae as a whole are extern.il 

 (jalaxies. When the i-pectroscope revealed the 

 gaseous nature of many of them this view was 

 generally abandoned, and it was supposed that all 

 the nebulae were within our Gala.xy. Mr. R. A. 

 Proctor strongly supported the latter hypothesis, 

 arguing that as we cannot resolve all parts of oiu- 

 own Galaxy it is extremely unlikely that we can see 

 external ones. He seems to have overlooked the 

 consideration that bodies which have sensible discs 

 do not lose in surface-brightness, but only in size, 

 when the distance is increased (assuming that no 

 light is absorbed in traversing space). 



The ancient view is now being revived in many 

 (luarters, as far as the white nebulae (those with a 

 continuous spectrum) are concerned. Sir David Gill 

 recently advocated it in a lecture delivered befon 

 the Koyal Institution, and Astr. Xaclirichtcii . 

 No. 45.56, contams an article on the same subject b> 

 Professor F. \V. Very. He takes the great Andro- 

 meda nebula as his standard ; its longer axis 

 (neglecting faint outhnes) is 11 0'. He calls the 

 distance of this nebula one "Andromede." and 

 endeavours to find it on the following two suppos- 

 itions: — (1) that its real diameter is equal to that 

 of our Galaxy, its distance is si.xty Galactic radii ; 

 (2) assuming that Nova .-^ndromedae belonged 

 to the nebula, and that its intrinsic brightness 

 at maximum was equal to that of a Galactic 

 star of zero m.Hgnitude. its distance is twenty- 

 five Galactic radii. On the latter assumption it is 

 much smaller than our Gala.xy. Professor Very takes the 

 mass of the Galaxy as equal to twenty million suns, and 

 deduces that of the nebula as one and a-quartcr million suns. 



He takes the distance of'our Galaxy as sonn; sixty light- 

 years, which appears to be too small, seeing that according to 

 this value the Galactic stars should have large proper motions, 

 and these in reality are very small. On this basis, and 

 adopting the value twenty-five for the ratio of distances, he 

 takes the distance of the Andromeda nebula as one thousand 

 six hundred light-years. The smallest of the white nebulae have 

 diameters about one six-hundredth of that of the .Andromeda 

 nebulae, whence their distance would be a million light-years. 

 He finds some evidence for the absorption of light in space 

 from the fact that the smaller nebulae appear al.so to be 

 intriusicallv fainter (surface for surface). He takes the trans- 



mission through a distance of one ".Andromede" as 0-996. 

 Through six hundred and twenty-five .Andromedes it would be 

 0-082, or only one-twelfth of the light would reach us. 



Still another confirmation of the fact that the Galactic stars 

 are on the whole beyond the region of sensible proper motion 

 has been given in a paper by Mr. Bellamy in Monthly 

 Notices for November. He has examined the larger proper 

 motions of stars in the zone between 24° and 26° North 

 Declination, from pairs of plates taken at an interval of some 

 ten years, with the following result : — 



Mean 

 Galactic 

 Latitude. 

 4°-9 

 21 -2 

 .57°- J 

 58° -7 

 78° -7 



Mean No. 



"f Stars 



per Plate. 



315 



247 

 128 



85 



74 



Mean No. 



of P.M.s 



per Plate. 



5-9 



5-7 

 4-6 

 5-1 

 4-8 



November 14th. 

 X = 55\ 



Fkukk 

 Mars. 1911. 

 November 14th. 

 \ = 94 . 



Sketches made at 

 Flagstaff. 



NOTK.-Thc rugioil 



Only proper motions exceeding one-tenth of a 

 second per annum are included. It will be seen 

 that while there is a slight increase in the number 

 of i)roper motions near the Gala.xy, it is not at all 

 in proportion to the increase in the number of 

 stars, showing that the Galactic stars lie beyond 

 the region of easily detected motions. Professor 

 \'ery is conscious of the difficulty, but endeavours 

 to evade it by suggesting that the absolute velocities 

 of stars in the Galactic system are smaller than in 

 the Sun's neighbourhood, on the analogy of the 

 diminution of planetary velocities, as their distance 

 from the sun increases ; but it is to be noted that even 

 if we grant this as regards their absolute motion, 

 the motion of the solar system would still give them 

 a large apparent motion. It is fairly well established 

 that the sun moves through some four astronomical 

 units per amunn. which, if unforeshortened, w-ould 

 give a star at sixty light-years distance an apparent 

 motion of one-fifth of a second per annum ; the 

 Galactic stars certainly show no motion approaching 

 this amoimt, whence it appears certain to me that 

 the Galaxy is far more than sixty light-years distant, 

 so that all Professor X'ery's estimates of Nebular 

 distances would need multiplication by a consider- 

 able factor. 



It is. of course, by no means certain that, e\en if 

 the white nebulae are composed of stars, they are 

 external Galaxies : they may well be miniatures of 

 the Galaxy included within its limits. The fact that 

 these nebnlae as a whole shun the Galactic Circle, 

 and are somewhat clustered about its Poles, presents 

 a considerable difficulty to the theory of their being 

 external. 



iK froM. 



PHOTOGRAPHS OF MARS,— Professor Lowell 

 has sent me three plates, each containing twenty exposures of 

 Mars. The first was taken on October 11th by Mr. Slipher 

 (longitude of centre of disc 70°). It shows Aurorae Sinus, 

 Lacus Soils. Tithonius Lacus. .Argyre, and traces of several 

 canals. The pair of plates taken on November 14th (longi- 

 tudes 55" and 94° respectively! show the same general 

 region of the planet (see Figures 40 and 411; their special 

 interest lies in the white patch at the bottom of the 

 disc, to the right of the polar cap, which Professor Lowell 

 considers to be morning hoar frost : comparison of the two 

 pictures shows that it does not move on with the surface 

 details, but clings to the morning limb, and this certainly 

 supports the hoar frost theory. The plates bring out much 

 variety in the depth of shading of the Maria, and .show some 

 indication of the canals across these ; the sketches given here 



