To6 



NA TURE 



June 2, 1892 



It will be seen that our investigations land us in tremendously involved state of the problem may be 



several astronomical questions of the greatest interest, I gathered froni the fact that the authorities are not yet 



and that the study is one in which modern computations, 1 decided whether many of the dates really belong to a 



with the great accuracy which the work of Leverrier and 1 fixed or a vague year ! 



Fig. 3. — The conditions of the heliacal rising of Sirius fr)m 4000 b.c. to 600 a.d. The diagram shows (i) by white horizontal lines, the Gregorian 

 and Julian dales for the rising at Thebes and at Memphis. (2) By the full diagonal line the Julian date of the solstice or beginning of the inunda- 

 tion in each century, at a point of the river near Memphis. The fainter lines show the Julian dates for other places where the time of the 

 beginning of the fljod differs by three days from the Memphis dates. The interval between each line represents a difference of three days 

 in the arrival of the flood (3) The interval in days between the heliacal rising and the inundation at different periods and at different 

 points on the river. This can be determined for each century by noticing the interval between the proper diagonal line and that indicating the 

 heliacal rising. (4) By dots at the top of the diagram the commencement of the Sothic period as determined by Oppolzer, Biot, and the author. 



Others give to them, can come to the rescue, and eke out 

 the scantiness of the ancient records. 



To consider the subject further, we must pass from the 

 mere question of the year to that of chronology generally, 



Let us, rather, put ourselves in the place of the old 

 Egyptians, and inquire how, out of the materials they 

 had at hand, a calendar could be constructed, in the 

 simplest way. 



M^^3Boc aMiBpSM i^HBE8Hw^^B8B88iS88BMBW^Kfl^BI 



*™^BJ!l^Mn"™^^1'^KM^r^MH!^^^*^r"8888M8 ™^ ^^^^^" 



miBiLPHuiittAfitaH 



Fig. 4.— The distribution of the ist of Thoth (representing the rising of Sirius) among the Egyptian months in the 1460-year Sothic cycle. 



but in doing so I shall limit myself to the more purely 

 astronomical part. To go over the already vast literature 

 is far from my intention, nor is it necessary to attempt to 

 settle all the differences of opinion which exist, and 

 which are so ably referred to by Krall in his masterly 

 analysis, to which I own myself deeply indebted. The 



NO. I I 79, VOL. 46] 



To make what follows clearer, it will be well to con- 

 struct another diagram somewhat like the former one. 



Let us map out the 1460 years which elapsed between 

 two successive coincidences between the ist of Thoth in 

 the vague year and the heliacal rising of Sirius at the 

 solstice, so that we can see at a glance the actual num- 



