ii6 



NATURE 



[November 14, 191: 



Nova (.Icminorum, No. 2 (1912), made between March 

 12 and the end of May, arc published and discussed 

 by Herr J. Fischer-Petersen in No. 460S of the Astro- 

 n'omisihe Nachrichten. The Hght-curve shows oscilla- 

 tions somewhat similar to those of Nova Persei in 1901, 

 but of less amplitude and longer period. The maximum 

 matrnitude, 3'8, was reached on March 14, and then 

 there was an abrupt fall, to s'4, on March 16; subsidiary 

 maxima occurred on March 24, 30, April 3 and q, 

 that on the first-named date being very marked 

 (mag. =4'8). .After .'\pril 9 the undulations of the 

 curve are very small. 



The D..\ri.: SiRLCTURitS in the Milky Way. — An in- 

 teresting paper full of suggestion as to the structure 

 of the universe is contributed by the Rev. T. E. 

 Espin to No. 4, vol vi., of the Journal of the Royal 

 .-Vsironomical Society of Canada. Mr. Espin recalls 

 Caroline Herschel's idea that a blank region in Scorpio 

 was believed by Sir William Herschel to indicate 

 "something more than a total absence of stars," and 

 then, bv the examination of other blank regions, he 

 proceeds to show that in all probability there exist in 

 the heavens masses of dark, light-absorbing vapours, 

 which hide from us the light emitted by stars or parts 

 of nebute in the background. The photographic 

 evidence seems almost irrefutable, it being difficult to 

 explain otherwise such observations of Dr. Kopff's that 

 " nearly all faint stars have disappeared from the 

 immediate surroundings of these nebulae, though they 

 are ten times more numerous, both in the nebulae 

 and far outside." But if we suppose the bright 

 nebute which are shown on our photographs to have 

 marg-ins which are too diffuse to become illuminated, 

 yet dense enough to absorb, the difficulty is removed, 

 and if this absorbing margin, or extension, is pro- 

 jected, by the position of our view-point, on to the 

 main body of the bright nebula, the "holes" and 

 "lanes" observed in such nebulae are similarly ex- 

 plained, k number of beautiful photographs to illus- 

 trate Mr. Espin's article are reproduced. 



Dr. Chant also has a paper in tlie same journal, 

 dealing with nebulae and their forms, and this, too, is 

 illustrated by many interesting reproductions. 



STELL.^R ACTINOMETRY AT THE YeRKES OBSERVATORY. 



— A paper of great importance to astropliysicists and 

 workers in stellar photometry is published by Mr. 

 J. A. Parkhurst in No. 3, vol. xxxvi., of The Astro- 

 physical Journal. For many years Mr. Parkhurst has 

 been working on the relations existing between photo- 

 graphic and visual magnitudes, and has published 

 details of a method whereby both could be measured 

 photographically. He now publishes the results of a 

 much more extended research, and gives both the 

 photographic and visual magnitudes for some 650 

 stars, down to magnitude 7'5, in the Potsdam Photo- 

 metric Durchmusterung, from 73° to the pole. The 

 photographic magnitudes were measured from extra- 

 focal "images on Seed 27 plates, and the "visual" 

 from reflector plates taken in the focus on colour- 

 sensitive plates, and with a specially prepared colour- 

 filter; Mr. Parkhurst fully describes the ingenious 

 methods of eliminating or determining the numerous 

 errors inherent to the observations. Then in his cata- 

 log-ue he gives the colour index of each star and, 

 where possible, the type of spectrum ; comparisons 

 with the results obtained by other observers show fair 

 agreement. The relation between spectrum and colour 

 index, using the Harvard classification for the former, 

 is best represented by a straif^ht line, the differences 

 being- so slight as not to warrant the introduction 

 of anv complex curve to show the relation. There 

 were '02 stars in this catalogue bright enough to give 

 spectra which could be classified, and, of these, exactly 



NO. 2246, VOL. 90] 



half belong to the types B„ to F„, and half to types 

 F| to M; 196, or 40 per cent., are of the A type. .Vt 

 the nearest approach to the galaxy, viz. 10° in R.A. 

 ih., each field showed some ten or twelve white stars, 

 while at the greatest distance from it, viz. 44° in R.A. 

 i3h., there were onlv two or three white stars per 

 field. 



THE IRON AND STEEL INSTITUTE. 



THE autumn meeting- of the Iron and Steel Insti- 

 tute, which was held at Leeds on September 30 

 and October 1-4, may fairly be described as a " practical 

 man's " meeting, for although the programme con- 

 tained approximately an equal number of "practical" 

 and "scientific" papers, those read and discussed at 

 the meeting belonged entirely to the former class. 

 While this is no duubt satisfactory to a large number 

 of members of the institute who take rather less 

 interest in scientific metallurgy than might fairly be 

 expected of them, it is rather hard on the authors of 

 scientific papers and on those members who were 

 attracted to the meeting by the array of such papers 

 on the programme. It is true that on other occasions 

 the programmes have erred in the opposite direction, 

 and it may be hoped that at future meetings a 

 judicious blending of both types of papers may be 

 brought up for discussion. 



-Among the papers relating to steel-wnrks practice, 

 the greatest interest and importance attaches to those 

 dealing with the question of the production of sound 

 ingots. Sir Robert Hadfield, F.R.S., who presented 

 papers on a method of producing sound ingots and 

 on a new method of revealing segregation in steel 

 ingots, introduced the subject by referring to the 

 series of alarming rail- fractures which had occurred 

 in America during the exceptionally severe 

 weather of last winter. These failures, and others 

 which occur under less severe conditions, he is 

 inclined to ascribe to unsoundness in the steel ingots 

 from which the rails are rolled. .According to the 

 treatment and additions which a steel has received, 

 the resulting ingot may suffer from unsoundness of 

 one of two distinct types ; the ingot may be more 

 or less full of cavities or blow-holes of varying size 

 and distribution, and in that case it is a non-settling, 

 non-piping steel in which gases have been liberated 

 during solidification in the mould. On the other 

 hand, by suitable additions of small quantities of 

 silicon or of aluminium, the steel may be rendered 

 "solid" or "settling" in the sense that the ingot 

 will be free from "blow-holes or small distributed 

 cavities, but it will — in the absence of special treatment 

 — have a deep central cavity or "pipe," the existence 

 of which results either in the discarding of a large 

 proportion of the finished steel by the rejection of the 

 upper portion of the ingot, or, if the piped portion 

 is not sufficiently discarded, an unsound rail may be 

 rolled from it, possibly with disastrous consequences. 



In one of his papers Sir Robert Hadfield suggests 

 a method of studying the formation of such pipes by 

 pouring molten copper into the ingot at a certain stage 

 of its solidification. He illustrates this method by 

 coloured sections of ingots thus treated, but in the 

 discussion Dr. J. E. Stead, F.R.S., pointed oijt that 

 the copper when poured in will partly alloy with the 

 still molten steel, and will then, by its greater density, 

 produce an upward displacement of the remaining 

 liquid steel, so tliat Hadfield's pretty method is really 

 only applicable if the copper is introduced immediately 

 after the complete solidification of the steel. Even if 

 introduced earlier, however, the copper makes it pos- 

 sible to trace the order in which the various parts of 



