Thus it comes to pass that
solar days, or the intervals elapsing between one return of the sun to
the meridian and another, are by no means equal. So a mean of their
lengths is taken by adding them up for a year, and dividing by 365;
and the quantity to be divided to or subtracted from the instant of
"apparent noon" (when the sun dial shows 12 o'clock), is set down in the
almanac under the heading of "The Equation of Time." We may, however,
here conceive that it is noon everywhere in the northern hemisphere when
the sun is due south. Now the earth turns on her axis from west to east,
and occupies 24 h. in doing so. As all circles are conceived to be
divided into 360 deg., it is obvious that in one hour 15 deg. must pass beneath
the sun or a star; 30 deg. in two hours, and so on. The longitude of
Kassassin is, roughly speaking, 32 deg. east, so that when the sun is due
south there, or it is noon, the earth must go on turning for two hours
and eight minutes before Greenwich comes under the sun, or it is noon
there, which is only another way of saying that at noon at Kassassin it
is 9 h. 52 m. A.M. at Greenwich. It is this purely local character
of time which gives rise to the seeming paradox of our being able to
receive news of an event before (by our clocks) it has happened at all.
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