442 SEC. 11. ASTRONOMY. 



which also act on the average length of the mean solar year of the earth), it 

 can be proved that a much greater mistake than two days will ensue for the 

 now existing period of decrease of the average length of the lunar month. 



TABLE VI. In this table the calculation according to Epacts will be 

 advantageously replaced by a new calculation, in which lunar numbers will 

 be used. 



TABLES VII. and VIII. In these tables greater simplicity and accuracy 

 will be attained for our Calendar, as all necessary " corrections " will be 

 adopted every secular year, as occasion may require, and not in accordance 

 with a predetermined cycle as in the Gregorian Calendar. Easter can then 

 either be maintained as a movable feast or become a fixed one, as it may 

 be found desirable by modern astronomers and statesmen. 



1924a. Calendar for Two Thousand Years. 



M. Georges Sarasin, Geneva. 



Lithographed sheet, framed and glazed, permitting the sight, by three 

 openings, of portions of a second lithographed sheet which is capable of move- 

 ment round a fixed centre. These lithographed sheets are divided into sectors 

 of a circle radiating from a common centre, which is at the same time the 

 centre of motion of the second. They are covered with figures and expla- 

 nations. An inscription denotes briefly the method of use. 



If, by the motion given to the central disc, the two figures which express 

 the tens and units of a year, and the figure which constitutes or the 

 two figures which constitute the hundreds (whether according to the Grego- 

 rian or Julian style), be brought into the same sector in such a way that 

 the latter be to the left and the former to the right, the calendar of that year 

 will be given on the lower portion of the sheet. The days of the week 

 will correspond to the days of the month in the radial direction, and to 

 the months in the circular direction, whichever of the two styles may have 

 been chosen. There is no occasion either to give a new movement to the disc, 

 or to take into consideration the dominical letter, except as serving to indi- 

 cate the groups of years. Two of these data being given, the third may be 

 found. When the three data are given, the years may be found, which, since 

 the Christian era, have possessed them together. 



The months of January and February are distinct according to whether it 

 be a bissextile or ordinary year that is in question. In the former case, the 

 tens and units figures, divisible by four, are separated by an empty space from 

 the preceding in the table of years. A third designation of the two above- 

 mentioned months is also perfectly suitable to the two classes of years, if the 

 date of the year immediately preceding be formed by the movement of the 

 disc. 



It may also be ascertained to what day of the ordinary week corresponds 

 any date during the thirteen years of the Kepublican style which followed the 

 year 1792, by taking for the hundreds portion the zero of the Julian style. 



1924d. Reproduction of the Books on Astronomy, 



written by Dr. Alonso el Sabio, 13th century, from the original 

 MS. at the Escorial. Academia de Ciencias, Madrid. 



"Libros del Saber de astronsmia del Hey Don Alonso el Sabio" 5 vol., gr. 

 in fol., Madrid. 



These volumes contain an extensive account of astronomical science in the 

 13th century, the plates reproduce among other details the constellations there 

 known, and the astronomical instruments used at the time. 



