*

On coming home I found that I had made an error in the first edition of
the "Physical Sciences," in giving 365 days 6 hours as the length of the
civil year of the ancient Egyptians. My friend Mr. Hallam, the
historian, wrote to me, proving from history and epochs of the
chronology of the ancient Egyptians, that their civil year was only 365
days. I was grateful to that great and amiable man for copies of all his
works while he was alive, and I am obliged to his daughter for an
excellent likeness of him, now that he is no more.

FROM HENRY HALLAM, ESQ., TO MRS. SOMERVILLE.

WIMPOLE STREET, _March 12th, 1835_.

MY DEAR MADAM,

As you will probably soon be called upon for another edition of your
excellent work on the "Connexion of the Physical Sciences," I think
you will excuse the liberty I take in mentioning to you one passage
which seems to have escaped your attention in so arduous a labour.
It is in page 104, where you have this sentence:--

"The Egyptians estimated the year at 365 d. 6 h., by which they lost
one year in every 14,601, their Sothiac period. They determined the
length of their year by the heliacal rising of Sirius, 2782 years
before the Christian era, which is the earliest epoch of Egyptian
chronology."

The Egyptian civil year was of 365 days only, as we find in
Herodotus, and I apprehend there is no dispute about it. The Sothiac
period, or that cycle in which the heliacal rising of Sirius passed
the whole civil year, and took place again on the same day, was of
1461 years, not 14,601. If they had adopted a year of 365 d. 6 h.,
this period would have been more than three times 14,601; the excess
of the sidereal year above that being only 9' 9", which will not
amount to a day in less than about 125 years.

I do not see how the heliacal rising of Sirius in any one year could
help them to determine its length. By comparing two successive years
they could of course have got at a sidereal year; but this is what
they did not do; hence the irregularity which produced the canicular
cycle. The commencement of that cycle is placed by ancient
chronologers in 1322 A.C. It seems not correct to call 2782 A.C.
"the earliest epoch of Egyptian chronology," for we have none of
their chronology nearly so old, and in fact no chronology, properly
so called, has yet been made out by our Egypt