238 



DISCOVERY 



line spectrum, tlic lines characteristic of nebuhc 

 come into prominence. The new star, in fact, appears 

 to be transformed into a nebula in the later stages of its 

 decline ; while, at a still later stage, the spectrum 

 becomes similar to that of the Wolf-Rayet stars. Thus, 

 in 1902, Pickering found the spectrum of Nova Pcrsei 

 to be nebular ; five years later, Hartmann at Gottingen 

 discovered that the spectrum was essentially identical 

 with that of a Wolf-Rayet star. Some years ago, the 

 spectra of four novje were closely studied by Messrs. 

 Adanis and Pease at Mount Wilson. By July 1914 

 they noticed that the two oldest, Nova Auriga: and 

 Nova Persei, had become Wolf-Rayet stars, and by 

 April 1915 Nova Lacertae and Novas Geminorum had 

 become similarly transformed. In connection with 

 this discovery Adams and Pease remarked that " this 

 identity of spectrum, taken in connection with the 

 well-known agreement of distribution, relative to the 

 Milky Way, of novse and Wolf-Rayet stars, makes it 

 probable that at least a portion of the latter are Wolf- 

 Rayet stars in the later stages of their histo^^^" 



The recent work of Mr. Van Maanen, the distinguished 

 Dutch astronomer, has shown that a number of the 

 \\'olf-Rayet stars which form the nuclei of planetar\' 

 nebulae are of feeble absolute magnitude and, therefore, 

 presumably of small mass. This fact is difficult to 

 reconcile with the order of stellar evolution as sketched 

 by Russell, and would suggest that there is an alter- 

 native path of evolution, and that some, at least, of 

 the dwarf stars, especially those abnormal stars of 

 which a few have been found in recent years, have 

 developed out of planetary nebute, which in their 

 turn have been the products of celestial catastrophes, 

 either of collisions between two or three feebly luminous 

 stars, or of encounters of stars with nebulous matter. 

 Russell's hypothesis, however, accounts for the 

 physical condition, brightness, volume, and mass of 

 the overwhelming majority of the stellar bodies, and 

 at present holds the field against all other cosmogonic 

 theories. 



Wliat of the time-scale of stellar evolution ? The 

 periods of time required for the stars to pass through 

 their various stages appear to be so enormous that in 

 tr^'ing to conceive them — to quote Horace Walpole's 

 dictum in regard to the work of Herschel — " one's 

 imagination cracks." Dr. Shapley's study of the stars 

 in the nearer clusters, 20,000 light-years ' away, and 

 those in the most distant systems, 220,000 light-years 

 removed from our earth, has shown that the stars in 

 the one cluster seem to be at the same stage of develop- 

 . ment as the stars in the other, which indicates that 

 200,000 years is a negligible quantity in the life of a 

 star — a mere tick of the clock. Recent studies of 



' A light-year is the distance travelled by light in one year. 

 About 5,860,000,000,000 miles. 



stellar evolution abundantly confirm the geological 

 estimates of the vast age of the earth. Periods of 

 thousands of millions of years are not extravagant 

 estimates of the age of our own world. What, then, 

 must be the age of the Sun ? How many tens or 

 hundreds of thousands of millions of years have elapsed 

 since the Sun was a red giant, flickering feebly for the 

 first time out of the dim night of the primeval chaos ? 



BIBLIOGRAPHY 

 Sir William Herschel : Collected Scientific Papers. 

 Sir William Huggins : Scientific Papers. 

 A. S. Eddington : Stellar Movements and the Structure vj the 



Universe. 

 H. N. Russell : " The Spectra and other Characteristics of the 



Stars." {Popular Astronomy, vol. xxii.) 

 H. Shapley: " Studies based on Colours and Magnitudes in 



Stellar Clusters." (Mount Wilson Contribution, No. 167.) 

 A. Fowler: Presidential Address to R.A.S., in Monthly 



Notices, vol. Ixxxi, No. 4. 



The Roman Calendar 



By W. R. Halliday, B..\., B.Litt. 



Professor of Ancient History in the Universilij of Liverpool 



It is, curiously, seldom that familiar words in ordinary 

 use convey the associations of their literal meaning, 

 and while many readers are probably aware, if they 

 stop to consider it, that September means " the seventh 

 month," few probably have noticed the anomaly of 

 calling the ninth month of the year by this name. 



The calendar month is, of course, part of the heritage 

 bequeathed by the Roman Empire to European 

 civilisation. At first sight, however, the problem 

 is no nearer solution, for the Roman Empire, too, began 

 its official year upon January the first. Earlier, when 

 Rome was still a repubhc, at any rate after 153 B.C., 

 it was upon the first of January that the two consuls, 

 the annually appointed magistrates who constituted 

 the chief executive of the State, entered upon their 

 duties. But as the names of our months still testify, 

 the Roman year had originally begun in March, the 

 month of spring, " when winter's rains and ruins are 

 over," when the citizen-farmer looked for\vard to the 

 agricultural prospects of the year, and the State to 

 the needs of the summer campaign. Appropriately 

 this is the month of Mars, who was both the god of 

 husbandry and the god of war. There follow April, 

 " the month in which things open," May, " the month of 

 growing," and June, "the month of rip-?ning." July 

 and August owe their present names to Julius Caesar 

 and Augustus ; originally they were called Quintilis, 

 the fifth, and Sextilis, the sixth month respectively. 

 September, October, November, and December are 

 similarly numerical names. Januar}-, when the days 



