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sliadow was longer than it was at other periods. In order to 
record these phenomena, and the better to trace their cause, 
they simply set up a pole in the ground, and marked tho 
length of its shadow at regular intervals.* 
They soon found that the noon-day shadow increased in 
length day by day until it attained a certain measurement, and 
that then it remained unchanged for a few days ; after this it as 
regularly decreased until it arrived at its shortest dimensions, 
and then again stood still for a while before resuming its diurnal 
increase. 
The period when it was the shortest was called the summer 
“ solstice the Sun then “ stood still,” high in the heavens, 
and its heat was the greatest. The longest noon-day shadow 
constituted the winter “ solstice,” and the duration from either 
of these phenomena to its recurrence was a year. 
It was found also that about midway between these periods 
(the summer and winter solstices) there were two others, when 
the day and night were equal, and these two periods were 
known as the equinoxes, all these terms being still employed 
by astronomers. 
In like manner did the ancients measure off the gnomon’s 
shadow from the Sun’s rising until his setting, and employ it 
to denote the time of the day. Thus, we are informed that 
“ a person was invited to dinner by asking him to come when 
the shadow of the gnomon was so many feet long and, as 
in our day, we have a “ Greenwich time ” for our clocks, so 
are our ancestors said to have had a standard measure by which 
their gnomons were regulated. 
The changes referred to, in the relative position of the Sun 
and Earth, offer no problem to our modern astronomers, who 
know that these appearances are due to the annual revolution 
of the Earth round the Sun, and the daily rotation of the 
former on its own axis. 
But to the dawning intellect of the shepherd astronomer 
the consideration of these phenomena was fraught with many 
difficulties, for he believed the firmament to be a solid sphere in 
which the heavenly bodies were firmly set, and with which 
they, therefore, revolved around the Earth as a centre. How, 
then, could the Sun deviate from its regular course, now 
rising and setting in one part of the heavens and now in 
another, whilst the constellations (for, from the earliest ages, 
the fixed stars were mapped out in groups) always maintained 
the same relative position in the firmament, rising and setting 
* In common with many astronomical discoveries, the earliest application 
of the sun-dial (or “ gnomon”), is buried in obscurity. It is supposed to have 
been invented by the Babylonians. 
