September i, 1910] 



NATURE 



■16 



account for the result that the velocity now determined is 

 some 2 km. per sec. greater than that found by Hough 

 and Halm, who employed many stars relatively near to 

 our svstem ; tentatively, it is suggested that these proximate 

 stars appear to participate "o some extent in the sun's 

 motion through space. 



.K remarkable feature of the results is that the solar 

 velocitv, relatively to the stars near the apex, is some 

 10 km. per sec. less than the velocity relative to those 

 near the antapex, separate solutions giving —18-38 km. 

 and —28-38 km. respectively. It is suggested that this 

 difference may be due to the stars near each point, or 

 near both, belonging to the two great star streams. The 

 mean value given as the definitive result of the paper is 

 ii=— 23-3 km. per sec. 



As further results, it was found that the average radial 

 velocitv of the stars, independent of the sun's motion, is 

 -6-3 km. per sec, and that the average parallax of the 

 sixty-one stars employed is 0-00924". 



Par.allax of Fovrtii-type St.ars. — The question of the 

 absorption of light in interstellar space led . Prof. Kapteyn 

 to look for classes of stars of which the probable distances 

 are very great ; such stars would best indicate any exist- 

 ing absorption. The fact that the proper motions of 

 fourth- and fifth-type stars are, so far as is known, in- 

 sensible, suggested that such stars would have extremely 

 small paralla.xes ; therefore Prof. Kapteyn calculated the 

 probable average parallax for some 120 stars of this type 

 from data determined by Mr. Norlund at Copenhagen. 



The result is striking, for the average parallax of these 

 fourth-type stars is found to be extremely small, 0-0007", 

 and does not exceed the probable error. Taking a previous 

 result for the selective absorption in space, the quantity 

 (photographic — visual magnitude) must amount, for these 

 stars, to at least half a magnitude ; it may be much 

 greater. Therefore, to be satisfactory, any interpretation 

 of the spectra of these stars cannot neglect the effect of 

 the possible light-absorption in space. 



For comparison. Prof. Kapteyn computed the probable 

 average parallaxes of other types and for Orion stars of 

 magnitude 5-0; he found the value 0-0068" + 0-0004", which 

 agrees satisfactorily with the value 0-0064" determined, by 

 an absolutely different method, in the discussion of the 

 ^un's velocity published by him, in collaboration with 

 Prof. Frost, in the same number of the Astrophysical 

 Journal (No. i, vol. xxxii.). 



TiiF. Maximum of Mira in 1909. — Two papers dealing 

 with the maximum of Mira in 1909 are published in No. 

 4434 of the .istroiiomische Nachrichten. In the former 

 Prof. Nijland discusses his observations at Utrecht, which 

 covered the period July 20, 1909, to March 3, and finds 

 that a maximum, of magnitude 3-1, took place on 

 -September 7, 1909. This agrees with Guthnick's 

 ephemeris, and gives a period, since last maximum, of 

 33b days. 



In the second paper Mr. Ichinohe discusses the observa- 

 tions made by him at the Tokio Observatory during 

 approximately the same period. .According to him, the 

 maximum took place on September 3, nearly four days 

 before the predicted epoch, and the magnitude was 3-2. 



The .Study of Dolble Stars for Amateurs. — Possessors 

 of small instruments desiring to take up a useful study 

 will find an interesting article by Mr. G. F. Chambers in 

 the .\ugust number of Knowledge and Scientific News. 

 'I'his is the first of a series of articles on double stars, and 

 in it Mr. Chambers discusses the question as to what 

 constitutes a double star, and also pays attention to the 

 question of coloured doubles. 



Metcalf's Co.met, 1910/). — F'urther observations of, and 

 a continuation of the ephemeris for, Metcalf's comet are 

 published in No. 443^ of the Astronomiscbe Nachrichten ; 

 the following is an extract from the ephemeris : — 



Ephemeris 12/1. M.T. Berlin. 



1910 a (1910) 5. (igio-o) log r log A Mag. 



h. m. 



Sept. 2 ... 15 37-5 ... -fie 437 ... 0-2886 ... 0-3027 ... 10-9 

 ,, 10 ... 15 32-4 ... -1-17 3-0 ... 0-2897 ... 0-3^42 ... ii-o 



,, 18 ... 15 29-4 ... +17 20-6 ... 0-2918 ... 03614 ... II -2 



NO. 2 131, VOL. 84] 



THE ROY.IL PHOTOGR.iPHIC SOCIETY'S 

 EXHIBITION. 



A S the New Gallery is now used for other than exhibi- 

 ■^~*' tion purposes, the Royal Photographic Society have 

 had to return to the Gallery of the Royal Society of 

 Painters in Water Colour, 5A Pall .Mall East, and hold 

 their exhibition earlier than usual. It is now open, and 

 closes on September 16. The trade and professional 

 sections have had to be omitted for want of room, and 

 the number of exhibits in the other sections considerably 

 reduced. The diminution in the number of exhibits may 

 cause disappointment to many who had prepared work for 

 the occasion ; but it is not an unmixed misfortune to the 

 visitor, for it seems to have led to a general raising of 

 the standard of quality. The pictorial section has a certain 

 measure of scientific interest, as the method of production 

 of almost all the prints is stated in the catalogue. They 

 indicate, therefore, in an intelligible way the possibilities 

 of the various processes, and at the same time a purchaser 

 knows what he is buying. The proportion of bromides 

 seems to be unduly large, and to indicate that many prefer 

 ease of production to an unassailable permanency. There 

 are two notable oil prints in colour, a still-life subject by 

 MM. S^eberger Fr^res, and " Carmencita " by Messrs. 

 Tilney and Corke ; but such work is on the very border- 

 land of photographv. 



In the colour-transparency section, the large majority of 

 the exhibits are autochromes. Some of these are of a 

 verv high standard of excellence. Mr. J. C. Warburg's 

 " Court of Honour, Ivorv and Azure," and " Grey 

 Hound Inn, Corfe," and ' Mr. Ellis Kelsey's " Beachy 

 Head, Reflections," show how truly it is possible to repro- 

 duce the effects of neutral and sober colours. The few 

 transparencies by the Dioptichrome Dufay Process are 

 chieflv of the garish colour type, and do not serve to 

 indicate the characteristics or possibilities of these plates. 

 The application of colour photography to natural history 

 and scientific purposes is illustrated by several trans- 

 parencies, and several photomicrographs of polarised light 

 effects show how well such slides can represent the actual 

 appearances. .\ set of nine slides of mineral sections in 

 polarised light by Mr. E. J. Garwood, made by the Sanger 

 Shepherd colour process, by the side of the autochromes 

 of similar subjects, demonstrates the superior brilliancy 

 of the Sanger Shepherd plates, and that this process, 

 although more trouble to work than the other, still holds 

 its own. 



In the natural history section, those exhibitors whose 

 work we expect to see vear bv vear continue to contribute. 

 Mr. Douglas English shows the black ratton, the probable 

 tvpe of the old English black rat, and the " plague " rat 

 of the East. Mr. William Farren shows five photographs 

 of the '■ whiskered tern " (taken in Spain), three show- 

 ing various phases of wing elevation in the act of alight- 

 ing. When Miss Turner 'and Mr. E. J. Bedford exhibit 

 rows of birds, each in the same row in a similar attitude 

 and sometimes a strange attitude, we should like to know 

 whether the birds were alive or dead when photographed. 

 .And this question might perhaps be asked with regard to 

 some other exhibits. .Among the entomological subjects, 

 special note mav perhaps be made of Mr. Hugh Main's 

 series of thirteen photographs of the metamorphoses of the 

 glow-worm in natural size, and Mr. P. J. Barrand's 

 '• queen wasp " in the attitude assumed during hyberna- 

 tion (x6). I 1 n 



The photomicrographs include many notable works. Ur. 

 G. H. Rodman's series of fourteen photographs illustrating 

 the life-historv and structure of the stick insects,, all low 

 magnifications (X3 to X 14) except the complete insects, 

 which are half size, and Mr. J. T. Holder's low magnifi- 

 cations of the twelve excellent sections, prepared, we 

 believe, by himself, showing the eyes and adjacent parts 

 of various' livmg creatures, deserve especial mention. Dr. 

 Max Poser's diatoms are, of course, good, but the interest 

 of them -would be much increased if the optical conditions 

 under which thev were photographed were stated- The 

 only apparent advantage of the enormous magnification 

 of nine thousand diameters of the Pleurosigma angidatiim 

 seems to be that all that is to be seen can be seen from 

 the other side of the room. His bacilli with flagella- 

 (xiooo) and his trvpanosome (X3000) are fine examples. 



