NAVIGATION. 17 



The building of the pyramids might therefore 

 have been at any time from 2480 B.C. to 2120 B.C., 

 or at any time from 3560 B.C. to 3200 B.C., to 

 suit the astronomical hypothesis. It was supposed 

 to be about 2100 B.C. when Sir John Herschel 

 first took up the question at the request of Col. 

 Howard Vyse. Now, from independent historical 

 evidence, 1 the date 3200 is the most probable. 

 The astronomical hypothesis cannot decide be- 

 tween these two dates, but if it were granted, it 

 would show that either of them is more probable 

 than any date between 3200 B.C. and 2480 B.C. 



1 6. The point on the horizon under the north 

 celestial pole is called the true North ; the true 



1 I am informed by my late colleague, Professor Lushington, that 

 "the whole chronology of early Egyptian times is perplexingly ob- 

 scure ; probably a dozen different systems have been built on equally 

 stable foundations. The latest attempt known to me to establish a 

 real basis is given in a little treatise by Diimichen, which is, I 

 believe, in the University Library ; it rests upon a comparison of the 

 fixed and vague year, found coupled with the name of a king which 

 is read as Bicheris, the sixth name in Manetho's list of the fourth 

 dynasty (the great pyramid dynasty). It would bring his time to 

 about 3000 B.C., and the pyramids from 100 to 200 years earlier. 

 It is found on the back of a huge papyrus just published at Leipzig 

 by G. Ebers in facsimile, a most important work, being the largest 

 and clearest written papyrus known, the contents chiefly medical.'* 



VOL. III. C 



