Capt, J. Herschel on a new form of Calendar. 357 



From III. follows P A = B E f> ^^ ^ =AJ)> 



and by construction F A = A 1) ; J 



from which results the equality of triangles ABE and ABD, 

 and therefore a=fi. Quod erat demonstrandum. 



F. G. Hesse. 



XLIV. On a new form of Calendar, by which the Year, or 

 Month, or Month-day, or Week-day may be readily found when 

 the other three components of a date are given. By Captain 

 J. Hekschel, R.E* 



THE Tabular Calendar annexed is perhaps as compact in 

 form and simple in use as is possible. Its use may 

 be stated thus : — Of the Year, Month, Day, and Week-day, 

 given any three to find the fourth. If we arrange these thus, 



[Ml 

 1) | W , it is clear that M and D, Y and W will each fix one 



_ Y~|~~ 



of the signs or hieroglyphs in the centre of the Table; and in 

 order that the day of the month shall fall on a certain week- 

 day in any given year, these signs must be the same. Thus, 

 Apr. | 



Mon. April 13, and Monday in 



take the case of 13 



1874 



1874, both indicate *. We have now only to suppose one of 

 these unknown to see that the sign indicated by the other pair 

 will show all the possible solutions. Thus ; — 



1. Y unknown ; M and D indicate * (or any other sign, ac- 



cording to the case) ; W and * indicate Y. 



2. M unknown ; Y and W indicate *; D and * indicate M. 



3. D unknown ; Y and W indicate * ; M and * indicate D. 



4. W unknown; M and D indicate *; Y and * indicate W. 



It is obvious that the signs are pure symbols for the occasion, 

 and are for this very reason chosen heterogeneous so as not to 

 have any meaning or order, per se. 



It is only necessary to add that, where the date is known to 

 fall in January or February of a bissextile year, the italic M is to 

 be used. Otherwise, or more generally, the italic M is only and 

 always to be used with a bissextile Y. Thus :~— 



* Communicated by the Author. 



