350 LAW AND FREEDOM IN HISTORY

magnitude of the corresponding unknown quantity in the other series.
Supposing, for example, that, in the history of civilization », a genera-
tion (3 were known to be separated from a generation a by a Time-
interval of, say, one hundred years, we ought then to be able to estimate
the psychic and social distance between these two generations, even if
their chronological relation to one another were the only information
about them that we had on record. Conversely, if we knew the psychic
and social difference between two generations, thanks to being informed
about their respective manners and customs by undated records such
as folk-tales handed down orally or the material evidence of stratified
artifacts disinterred by archaeologists, we ought then to be able to
estimate the chronological interval between them by inference, even if we
had not inherited or recovered any table of dates to tell us their chrono-
logical relation to one another in plain figures. The assumption that a
particular quantum of psycho-social change invariably takes the same
span of Time in accomplishing itself had become so unquestionable an
article of faith in the mind of at least one distinguished Modern Western
student of Egyptiac history that he actually rejected the chronological
data presented by Astronomy on the ground, not that this evidence
was dubious in itself, but that to accept it would mean accepting, in
consequence, the, to him, inadmissible proposition that the tempo of
psycho-social change in the Egyptiac World must have been notably
quicker during one period of two hundred years' length than it had been
during an immediately preceding period of an approximately equal
span.

'If we find that the heliacal rising of Sirius is noted in an Egyptian
document as falling in a certain month of a certain year in the reign of a
certain king, it would seem that by calculating the loss of days implied
we could discover the year B.C. to which the given year corresponds. On
this principle, by means of a statement in a papyrus found at Kahun, that
Sothis rose heliacally on the first of the month Pharmouthi in the seventh
year of Senusret III, it has been computed that this year was 1882 (1876)
or 1876 (1872) B.C., while from the same data another computer has
arrived at 1945 B.C. But there are many considerations which militate
against an unreserved acceptance of either of these dates, in the present
state of our knowledge. If the former date were accepted, the end of the
Xllth Dynasty would fall in 1788 B.C.1 But it will be admitted by all who
have studied the material for the history of the time that to allow only two
centuries for the period between Dynasties XII and XVIII is difficult. If
there are resemblances in culture between the Xllth. and the early reigns
of the XVIIIth Dynasty which argue a comparative proximity in time,
there are, on the other hand, differences which cannot be accounted for if
the distance is to be measured by no more than two hundred years. The
Xllth Dynasty itself lasted for two centuries. Are the changes observable
during its continuance in any way comparable to those which had come

1 The last (incomplete) year of the Twelfth Dynasty's regime would be, not 1788 B.C.,
but 1378 B.C., according to L. H. Wood's revision (in the Bulletin of the American Schools
of Oriental Research, No. 99, October 1945 (New Haven. 1945, A.S.O.R.), pp. 5-9) of
W. F. Ed^erton's chronology (in the Journal of Near Eastern Studies, vol. i (Chicago
1942, University of Chicago Press), pp. 306-14). R. A. Parker, in The Calendars of
Ancient Egypt (Chicago 1950, University of Chicago Press), p. 69, makes the last year
of the Twelfth Dynasty's regime 1786 B.C.—A.J.T.