74 



KNOWLEDGE 



[April 1, 1891. 



considerably from the results obtained by other observers. 

 The mean of seven other faii-Iy accordant detenninatious 

 of the parallax of Vega would give its intrinsic light- 

 giving power as 1'92. In any case the two stars are 

 evidently exceptional, and, as what we are seeking for is 

 an average i-esult, may well be left on one side, and then 

 the remaining stars do not differ extravagantly in bright- 

 ness. The mean Sirian star would then have a light- 

 giving power of 1'07; the mean Solar star of 1*8 ; a 

 result which I think may at least warrant us in saying 

 that the supposed superiority of First Type stars receives 

 no support from it. 



Yet another mode of attacking the problem is open to 

 us. Binary stars, the orbits of which have been deter- 

 mined afford a means, as Mr. Monck has pointed out, of 

 forming some idea of their relative brightness, if we as- 

 sume that all the stars in question are spheres of equal 

 density, and Mr. Gore, in his recent " Catalogue of Binary 

 Btars," has computed this relative brilliancy per unit of 

 surface for most of the fifty-nine stars whose orbits he 

 gives. The result is a curious one. All the stars are, as 

 Mr. Gore himself remarks, either First or Second Type, 

 and there is a well-marked and unmistakable superiority 

 of the First over the Second.''' Assuming all the stars 

 of equal density, the Sirian are about six times as 

 bright, surface for surface, as the Solar. From this we 

 may infer that the slight superiority in total radiating 

 power of the Solar stars is not due to greater extent of 

 photosphere in proportion to their mass, but that the very 

 reverse is the case ; so that the Solar stars do not merely 

 emit more light than the Sirian, but they are superior to 

 tiiem in a yet higher proportion, both in size and density. 

 If so, we may regard theorists as probably right when they 

 have placed the Second Type stars as belonging to a later 

 stage that the First ; but as wrong when they have re- 

 garded the Sirian stars as occupying the apex of the 

 curve, and stars like our sun as being well advanced on 

 the road to decay. 



* Except in the case of one star, y Leonis, which is clearly by 

 far the brightest star, surface for surface, on the assnmption men- 

 tioned above. 



A PERPETUAL CALENDAR. 

 In addition to the rules given in the last number for 

 finding the day of the week corresponding to any given 

 date New Style, we might have added some simple rules to 

 extend the use of Mr. Prince's table and calendar to dates 

 previous to 2nd September 1752, when the Old Style 

 of reckoning came to an end. The change of style was 

 effected in England by dropping the eleven days between 

 Wednesday the 2nd September 1752, and Thursday the 

 nth September 1752. If the eleven days had not been 

 dropped, the 14th of Sejitember would ha\e been on a 

 Monday ; therefore, in passing backwards from New Style 

 dates to Old Style dates, Thursday becomes Monday and 

 one jumps forward four days in the week, or backwards 

 three days. 



To find the day of the week on which an event happened 

 in the last century after the change of style, the rule given 

 in the last number was- — find the day of the week for the 

 corresponding day in this century, and go forward two days 

 in the week. From the beginning of the century to the 

 2nd September 1752, you must find the day of the week for 

 the corresponding day in this century and go forward six 

 days, which is equivalent to going back one day in the 

 week. 



Events which happened in the 17th century occurred on 



the same day of the week as that on which the bicentenary 

 of the event falls in this century ; thus, Evelyn mentions 

 that Ash Wednesday in the year 1661 was on February 

 27th. Turning to the table in the last number, w^e find that 

 the Dominical Letter for 1861 was F, and that the 27th 

 February 1861 was also on a Wednesday. To go back to 

 preceding centuries of Old Style reckoning we go forward 

 one day in the week for every century. Thus, events in 

 the 16th century which happened on a Sunday, have their 

 tercentenaries in this century on a Saturday. 



Mr. E. Er.skine Scott has sent us a Perpetual Almanack 

 and Calendar published by him in 1850, which, besides a 

 table for finding the day of the week corresponding to 

 any day of the year when the Dominical Letter is given, 

 gives a table with the Dominical Letter for every year, from 

 the Christian Era onwards, reckoning by either Old 

 Style or New — a table which will be found convenient 

 for determining the days of the week corresponding to dates 

 in foreign countries as well as in England. The Gre- 

 gorian or New Style was adopted in Rome in 1582; in 

 Paris, by taking ten days off' the Calendar, 15th December 

 1582. In Russia, Old Style is still in use. It now dif- 

 fers from the New Style by twelve days ; thus, the lath 

 of April 1891 in England corresponds to the 1st of April 

 in Russia. 



TABLE I. 



Me. Ekskine Scott's Table for finding the Dominical Leiter 



OR Letters for any Year, Old Style or New. 



Directions. — Look for the 

 given year at the top of the 



himdreds contained in the 

 Table, on the lelt for New 



