DISCOVERY 



237 



is the information which had been gained as to the 

 actual =izes of certain stars during the past few years. 

 In 1916 two very faint stars of rapid proper motion 

 were discovered, one by Professor Barnard at the 

 Yerkes Observatory, and the other by Mr. Innes in 

 South Africa. The small star in Ophiuchus detected 

 by Barnard proved to be one of the Sun's nearer 

 neighbours in space, its parallax being easily measur- 

 able. The luminosity of this small red star appears to 

 be only ^.sVij of that of the Sun, and its diameter 

 three-ninths. Mr. Innes' star — still nearer to our 

 system — appears to be about the same luminosity 

 and size. " It is," Dr. A. D. C. Crommelin has pointed 

 out, " in all probability very near the end of its career 

 as a star, and an opaque crust may be expected to 

 form over its surface comparatively soon." These 

 stars, then, are indisputably dwarfs. 



A still more striking piece of confirmatory evidence 

 was obtained in December of last year. In the course 

 of his address at the British Association in August 1920, 

 Professor Eddington, adopting the theory of Professor 

 Russell, made an estimate of the probable angular 

 diameters ^ of some of the brighter stars. " The star with 

 the greatest apparent diameter is almost certainly 

 Betelgcux, diameter 0051." On the night of 

 December 13, Messrs. Pease and Anderson succeeded in 

 measuring the diameter of this star by means of the new 

 interferometer attached to the great loo-inch reflector. 

 The angular diameter of Betelgeux — the first stellar 

 diameter ever directly measured — came out at 0045. 

 The parallax is known with some degree of accuracy, 

 and from this the actual size of the star can be com- 

 puted. The diameter appears to be not less than 

 273,000,000 miles, and the volume about 27,000,000 

 times that of the Sun. The existence of giant stars is, 

 therefore, no longer a matter of theory ; and Professor 

 Russell's hypothesis has been triumphantly vindicated 

 by observation. More recently the diameter of Arcturus 

 has been measured. The angular diameter is 0012, 

 in close accord with Eddington's estimate ; and the 

 linear diameter is about 19,000,000 miles, just its 

 theoretical size according to the theory of Russell. 



In presenting the Gold Medal of the Royal Astro- 

 nomical Society to Professor Russell, in February 1921, 

 Professor Alfred Fowler remarked that the theory " has 

 the great merit of simplicity and it violates no known 

 physical laws. RusseU has led us step by step from 

 the simple conception of giant stars to a consistent 

 explanation of a multitude of phenomena, so that the 

 scope of the theory has become almost as wide as 

 the universe itself." This is eminently true, yet the 

 hypothesis, while solving a multitude of problems, has 

 opened, or rather reopened, several others. What, it 



i The angle (in seconds) which the diameter subtends at 

 the earth 



may be asked, arc the place and function of the nebulae 

 according to this outline of the sequence of the stellar 

 evolution ? Russell's theory begins with the great 

 diffuse red giants, and this stage he takes to be the 

 earliest stage in stellar life. It so happens that the 

 nebulae, which since Herschel's time have been almost 

 universally regarded as the primeval world-stuff, 

 are usually to be seen in association with white and 

 blue, not red, stars. In the decisive words of Professor 

 Campbell, " Nebulje and red stars do not coexist. . . . 

 If you find a red or yellow star of normal type, do not 

 look for a nebula in apparent contact with it." The 

 jiroblem is still further complicated by the fact that the 

 Wolf-Rayet stars, a rare class akin to the B stars, are 

 closely related to nebuh-e, and that in many cases the 

 nuclei of planetary nebuLe are actually Wolf-Rayet 

 stars. Many temporary stars, too, in the later stages 

 of their history pass through a nebular and then a Wolf- 

 Rayet stage. 



Professor Russell would seem to incline to the view 

 that the irregular gaseous nebulae are not the pro- 

 genitors, but the products, of the hot B type stars. 

 It may be that these intensely hot gaseous masses, 

 expelled from the stars at their period of greatest heat 

 and activity, ultimately develop into planetary systems, 

 but if Professor Russell's theory is the true one, they 

 are not the parents of stars. The stars would appear 

 to be vastly older than the gaseous nebulse. Recent 

 investigation has, however, indicated the existence of 

 vast masses of dark nebulosity, particularly in the 

 vicinity of the galactic zone. This dark nebulous 

 material was first disclosed by the photographs of 

 Professor Max Wolf ; and latterly Professor Barnard 

 has discovered a large number of these " dark patches " 

 and has, indeed, compiled a catalogue of them. 

 Apparently, if Russell's theory be the true one, these 

 dark nebulae and not the bright, glowing gaseous 

 masses, such as that in Orion, constitute the primeval 

 chaos from which the stars are born. 



Another problem which has not yet been fully solved 

 is the place occupied by temporary stars in the scheme 

 of things. Time was when the appearance of a new 

 star was a rare phenomenon. A hundred years ago, 

 only about half a dozen authentic instances of the 

 appearance of new stars had been recorded in the 

 course of astronomical history. Within recent years, 

 however, owing to the closer watch kept on the heavens, 

 and the large number of celestial photographs which are 

 secured at the different observatories, many of these 

 " novae " are now known to have appeared, and several 

 are usually detected in the course of a single year. The 

 spectroscopic study of the brighter members of this 

 class has shown that, after the initial outburst which 

 gives rise to a temporary star, a certain sequence is 

 usually followed. After the appearance of a bright- 



