August 4, 1923] 



NATURE 



169 



The temperature reached at the maximum point 

 depends on the mass of the star : the greater the mass^ 

 the higher the temperature and the longer the stellar 

 life. Fig. 3 illustrates the careers of the sun and of 

 stars the masses of which have nearly the extreme values 

 found in Nature. Probably a star having a mass less 

 than one-tenth of that of the 

 sun would not become hot 

 enough to be seen, while Edding- 

 ton has shown that stars much 

 more than ten times as massive 

 as the sun would be unstable. 

 Only the most massive stars 

 can reach the B and Oe 5 stages 

 of the Harvard spectral se- 

 quence. The lighter stars, like 

 the suUj turn back at the A 

 condition, or even at a still 

 lower stage. 



Temperature appeared at first, in this great stellar 

 drama, to play a dependent role. The star developed 

 heat by contraction, and radiated heat into space. 

 So long as the amount of heat developed exceeded the 

 amount radiated, the tempera- 

 ture would rise, and when, 

 through retardation of contrac- 

 tion and increase of radiation, 

 the conditions were reversed, 

 the temperature would fall. 

 KThis view is satisfactory in 

 every respect but one — it indi- 

 cates a length of stellar life far 

 shorter than . geological and 

 )ther evidence makes it pos- 

 sible to admit. In order to account for the amount 

 )f heat which a star radiates during its immeasurably 

 Jong life, it is necessary to suppose that the heat 

 fenerated by contraction is supplemented by an 



enormous supply of energy from some other source. 

 Nothing is certainly known of the nature of this supply. 

 Possibly, as Eddington proposes, it is to be found in 

 the formation of heavier elements from hydrogen. 

 But, wherever the energy comes from, it is difficult to 

 avoid the hypothesis that it can be released only at 



Fig. 2. — Diagrammatic representation of the theoretical development of a massive star from an original 

 nebula to a final cold, dense body. The dotted curve is to be regarded as identical with the highest 

 curve in Fig. 3. 



the extremely high temperatures attained near the 

 centres of stars. Contraction raises the temperature 

 of a star up to a certain point, and then temperature 

 takes charge and sets free energy from the unknown 



Fig. 3. — Curves illustrating the course of evolution of stars of differing mass, showing that, the more massive 

 the star, the longer is its life and the greater is the range of temperature through which it passes. 



source at a rate almost equal to the rate of radiation, 

 so that the star is in a condition of approximate 

 equilibrium. It is a problem for the future to determine 

 the origin of the almost inexhaustible supply. 



Man and Scottish Animal Life.^ 



By Dr. James Ritchie. 



IN the opportunity it affords for the study of the 

 part man plays in the evolution of a fauna, the 

 animal life of Scotland stands alone. This is largely due 

 to a series of geological accidents : the Glacial Period, 

 which made a clean sweep of former faunas ; the post- 

 glacial continental land bridge, which allowed immigra- 

 tion from the mainland of Europe, and the subsequent 

 breaking of the continental connexion. Thus there 

 was isolated on the tabula rasa of Scotland a fair 

 sample of the post-glacial European fauna, which 

 henceforth was removed from the possibility of sub- 

 sequent migrations such as complicate the history of 

 continental faunas, and the later evolution of which 

 must in general be due either to the influence of 

 physical and organic changes limited in time and space, 

 or to the interference of man. 



The influence of man was itself strictly limited in 

 time, for the earliest human settlements so far recognised 

 in Scotland date back only to Azihan times. It was 

 also unequal in its incidence, gaining in intensity with 

 the passing of time. Thus during the Neolithic, Bronze, 



• Summary of an address delivered at the request of the Council to the 

 Royal Society of Edinburgh on July 2. 



NO. 2805, VOL. I 12] 



and early Iron Ages only some four of the larger mem- 

 bers of the original fauna disappeared — the giant fallow 

 deer, the lynx, the lemming, and the rat vole — and it 

 is doubtful whether the disappearance of any of these 

 was due to man's presence. We may say, therefore, 

 that when the Roman legions followed Agricola north- 

 wards through the marshes of Scotland in the early 

 years of our era, they found a fauna which, except for 

 the presence of primitive domesticated animals, differed 

 little in kind from that which greeted man on his first 

 arrival in Scotland some 8000 years before. But the 

 following centuries saw more rapid changes, which so 

 increased that by the sixteenth century many new 

 and important elements had been added, while most 

 of the larger members of the old fauna had been swept 

 away, with the extermination of such as the reindeer, 

 the elk and the wild boar, the brown bear and the 

 beaver, the great bustard, the crane and the bittern. 

 Nowadays the content and assortment of the fauna, 

 the relative numbers of its members and their dis- 

 tribution, show little resemblance to the conditions of 

 the original post-glacial immigrants. 

 The degree of man's interference may be compared 



