The evening times. [volume] (Grand Forks, N.D.) 1906-1914, 1911-09-25
(Manchester Guardian.)

To many people whose notions OF
time depend entirely OF the perform
ance of some clock or watch the ideas
associated with the determination of
time may come as a considerable sur
prise. 1t is long since Greenwich time
became the official time for Great Brit
ain, but the advent of railways and the
invention of the telegraph were need
ed to supply the strongest arguments
in its favor and the means of distri-
buting it. No terrestrial timekeeper
can be absolutely depended upon.
Some of the ancients relied on the
sun, dividing the period from sunrise
to sunset into twelve equal portions,
and ever now the sun is not to be ne
elected as a means of correcting GER
tain small cumulative errors. But it
is the regular rotation of the earth it.
self at a uniform rate which supplies
our observations with their standard
CLOCK" Assuming that the very small
apparent motions of the standard stars
relative to each other and the sun can
be satisfactorily eliminated, there is
practically a fixed background sur
rounding the earth, within which it
rotates, with small subsidiary motions,
such as mutation, which can also be al
lowed for.
For practical purposes day is
roughly measured by the earth's rota-
ton with respect to the sun, but in
the first place the suns distance is
not uniform, and moreover the earth's
axis of rotation is inclined at quite a
considerable angle to the plane of its
revolution round the sun. So that
the day as measured by the sun is not
uniform. Noon by the sun is about
half an hour earlier in November than
it in June. as may be see by the table
Of corrections to any well-regulated
sundiai. Moreover, time determined
by the meridian passage of the sun
would depend upon a single observa-
tion each day when it happened to be
fine at noon. More accurate observa-
lions and many more of them can be
obtained of what are called clock
stars. Hence it is the earth's rotation
with respect to the stars that Green.
witch relies upon for it's standard clock
and since the earth is moving round
the sun once a year in the same direc-
ton al that in which it rotates, it has
one less day in the year with respect
to the sun than it has with respect
to the stars.
These clock stars, which have been
kept under good observation since the
time of Flamsteed, the first astronomer
royal, have their motions known with
sufficient accuracy, and the nautical
almanac Office publishes a few years
in advance what is sometimes called
the Sailors Bible" from which the
time at which they cross the meridian
of Greenwich can be accurately found
every day.
Practically on every fine night some
of those stars are observed with the
meridian transit circle. That is to say
the time by the Greenwich standard
sideral clock when a clock star crosses
the meridian is electrically registered
by the observer. This time, when cor.
rected for instrumental errors and fol
the personal equation" of the OBJ
server, provides a simple means Of de,
termining the actual error of the sid
ereal clock, as the time given in tn,
nautical almanac differs from that act
ually. determined by the amount o
the clock error comparing one da.
with the next. The rate of the clocl
is inferred. and recourse is again hat
to the nautical almanac for the sid
ereal time Of mean" noon; i. e., tn,
time when the sun would be due soutl
If the earth's motion were uniform
Comparison of the mean solar clocl
with the true sidereal time soon show
the error of the former, and this /
corrected by electrical means, tn
force on its pendulum being increas
ed or diminished as may be found nee
essary until 1t is correct. This is don,
every day except Saturdays and publ
holidays before 10 a. M, at which hou
the time signal which goes to the post
Office at every hour is transmitted al
over the country. Every day withou
Exception the clock is corrected befor