DOI Seite / Zitierlink:
https://doi.org/10.11588/diglit.15#0222
THE ORIGIN OF THE WEEK. 209
suggests also the idea of numerical measurement.
And measures of length, surface, volume, and so
forth, could more readily have been derived in
ancient times from the moon's motions than in any-
other manner. In precisely the same way that now,
in Great Britain, all our measures,' without excep-
tion, are derived from the daily motion of the
stars, so in old times the more obvious motions
of the moon could have been used, and were pro-
bably used, to give the measures required in those
days.
1 Even our. measures of the value of money depend on the ob-
served motions of the stars. As I pointed out in my essay ' Our
Chief Timepiece Losing Time ' {Light Science for Leisure Hours),
' when we come to inquire closely into the question of a sovereign's
intrinsic value, we find ourselves led to the diurnal motion of the
stars by no very long or intricate path. ' For a sovereign is a coin
containing so many grains of gold mixed with so many grains of
alloy. A grain is the weight of such and such a volume of a certain
standard substance—that is, so many cubic inches, or parts of a
cubic inch, of that substance. An inch is determined as a certain
fraction of the length of a pendulum vibrating seconds in the latitude
of London. A second is a certain portion of a mean solar day, and
is practically determined by a reference to what is called a sidereal
day—the interval, namely, between the successive passages by the
same star across the celestial meridian of any fixed place. This
interval is assumed to be constant, and is in fact very nearly so.
Strangely enough, the moon, the older measure of time, is, by her
attraction on the waters of this earth, constantly tending to modify
this nearly constant quantity—the earth's rotation. For the rt sist-
ance of the tidal wave acts as a break, constantly retarding the
earth's turning motion—though so slowly, that 1,500 millions of
years would be required to lengthen the terrestrial day by one full
hour.
suggests also the idea of numerical measurement.
And measures of length, surface, volume, and so
forth, could more readily have been derived in
ancient times from the moon's motions than in any-
other manner. In precisely the same way that now,
in Great Britain, all our measures,' without excep-
tion, are derived from the daily motion of the
stars, so in old times the more obvious motions
of the moon could have been used, and were pro-
bably used, to give the measures required in those
days.
1 Even our. measures of the value of money depend on the ob-
served motions of the stars. As I pointed out in my essay ' Our
Chief Timepiece Losing Time ' {Light Science for Leisure Hours),
' when we come to inquire closely into the question of a sovereign's
intrinsic value, we find ourselves led to the diurnal motion of the
stars by no very long or intricate path. ' For a sovereign is a coin
containing so many grains of gold mixed with so many grains of
alloy. A grain is the weight of such and such a volume of a certain
standard substance—that is, so many cubic inches, or parts of a
cubic inch, of that substance. An inch is determined as a certain
fraction of the length of a pendulum vibrating seconds in the latitude
of London. A second is a certain portion of a mean solar day, and
is practically determined by a reference to what is called a sidereal
day—the interval, namely, between the successive passages by the
same star across the celestial meridian of any fixed place. This
interval is assumed to be constant, and is in fact very nearly so.
Strangely enough, the moon, the older measure of time, is, by her
attraction on the waters of this earth, constantly tending to modify
this nearly constant quantity—the earth's rotation. For the rt sist-
ance of the tidal wave acts as a break, constantly retarding the
earth's turning motion—though so slowly, that 1,500 millions of
years would be required to lengthen the terrestrial day by one full
hour.