DISCOVERY 



59 



the difficulties of University libraries and other in- 

 stitutions of like nature in keeping in touch with the 

 literature of science is a different problem — and one 

 which a little imagination and trifling cost in England 

 and other lately allied countries would easily solve. 

 And if it be not solved, it is fairly certain that the loss 

 to the sum of human knowledge, the set-back to 

 medical science in its arduous battle against disease. 

 and the stifling of the humane studies and arts, will 

 involve this tortured generation in a new offence 

 against the ages to come. 



***** 



We are getting superior in our attitude towards 

 elements, but the news of another one to add to their 

 short list is of some interest, if only to the man who, 

 with the stamp collector's instinct, wishes to see a set 

 complete. Two observers from Copenhagen, Coster 

 and Heresey, announced in Nature of January 20 

 their identification of a new element which they call 

 Hafnium. Its discovery is in some respects romantic. 

 In 1914 H. G. S. Moseley published his investigations 

 of X-ray spectra of elements. It was well known that 

 each element had a characteristic line in the spectrum 

 — that is to say that, when the element was heated to 

 incandescence and its light analysed with a prism, 

 dark lines on the patch of colour are typical of that 

 particular element. This fact has enabled us to 

 ascertain the composition of the sun and remote 

 stars ; but a fair amount of substance is necessary to 

 identify an element by these means. The use of 

 kathode rays, as they are called — the bombardment of 

 a crystal by electrons from an X-ray tube — produces 

 an equally characteristic spectrum on a sensitive 

 photographic plate. This method, however, is available 

 for minute quantities of the substance investigated 

 and is very accurate. Not only that — Moseley was 

 able to assign to each element a number, which he 

 associated with the number of electrons which rotate 

 round the core of the atom. In all ninety-two atomic 

 numbers were assigned, but there were six blanks in 

 his list. Sir James Walker prophesied that element 

 seventy-two, one of the blank numbers, would resemble 

 a rare metal zirconium — discovered in 1789 — in its 

 properties. This proves to be the case, for the new 

 element has been traced by X-ray analysis in an ore 

 containing zirconium. Elements forty-three and 

 seventy-five, among others, still await discovery, and 

 it is a remarkable fact that we know nearly all about 

 them, their properties and their weights in comparison 

 with other elements, from the work of Moseley ' and 

 his predecessors without ever having seen them. It 

 is just possible, though improbable, that they do not 

 e.xist on this planet of ours. If so, fresh opportunities 

 await, maybe, the first man to reach Mars ! 



' Introduction to Physical Chemistry , 1922. 



What are the Nebulse? 



An Astronomical Problem 



By the Rev. Hector Macpherson, M.A., 

 F.R.A.S., F.R.S.E. 



Twentieth-century research with telescope, spectro- 

 scope, and camera has emphasised the division of 

 the nebulEe into several sharply differentiated groups 

 or classes. First of all, there are the bright irregular 

 nebulas, of which that in Orion is the most prominent ; 

 secondly, and closely connected with these, the 

 dark nebula; ; thirdly, the planetary nebulae ; fourthly, 

 the spirals ; and fifthly, a class of small round 

 objects which were formerly classified with the 

 spirals, but obviouslj' differ from them in many 

 important respects. 



I. The Bright and Dark Nebulae 



The discovery that the bright irregular nebulas are 

 gaseous gave powerful support to the view that they 

 represented "worlds in the making," the material 

 which would be, in the course of ages, wrought into 

 suns and systems. This, indeed, appeared to be 

 placed beyond all doubt by the association of these 

 nebulous masses with the so-called " early-type " 

 stars. This association is one of the indisputable 

 facts of stellar astronomy. Wherever there is a great 

 nebulous region, the earlier or the blue-white types of 

 stars are found in an abnormally plentiful quantity, 

 and the chances are fairly strong that some of the 

 stellar spectra will contain bright lines. On the other 

 hand, nebulae and red stars do not exist near each 

 other. In recent years, however, the aspect of the 

 question has been completely altered by the formula- 

 tion of Professor Russell's theory of stellar evolution. 

 According to this hypothesis, which has been confirmed 

 both by theoretical investigation and observational 

 evidence, the blue-white stars are not the youngest 

 stars, but are suns in their prime, in the meridian of 

 stellar life. If the blue stars are not the youngest of 

 the suns, what, it may be asked, is the nature and 

 function of the diffused gaseous nebulosity ? 



The question has been still further complicated by one 

 of the most remarkable discoveries of recent years — 

 that of the second class of nebular objects — the dark 

 nebulae. Herschel drew attention over a century ago 

 to several dark spots in the galactic regions which he 

 referred to as " holes in the heavens," and Sir John 

 Herschel detected a number of others. During the 

 last century it was believed that these dark spots 

 were simply regions free from stars, and it is probable 

 that a number of them do represent vacant spaces. 

 In 1902, however. Professor Max Wolf remarked on 

 their symmetrical arrangement in regard to the stars 



