The turning of the earth upon its own axis every 24
hours, whilst it moves round the sun in a year, we may
conceive by the running pf a bowl on a bowling-green ;
in which not only the centre of the bowl hath a pro-
gressive motion on the green; but the bowl in its
going forward, from one part of the green to another,
turns round about its own axis.
The turning of the earth on its own axis makes
the difference of day and night ; it being day in those
parts of the earth whicji are turned towards the sun;
and night in those parts which are in the shade, or
turned from the sun.
The annual revolution of the earth in the ecliptic,
is the cause of the different seasons, and of the several
lengths of days and nights, in every part of the world,
in the course of the year.
The reason of it, is the earth's going round its own
axis in the ecliptic, but at the same time keeping
every where its axis equally inclined to the plane of
the ecliptic, and parallel to itself. For the plane of
the ecliptic inclinmg to the plane of the equator 23
degrees and a half, makes that the earthy moving



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Elements qf Natural Philosophy. 31 1

round in the ecliptic, hath sometimes one of its poles,
and sometimes the other, nearer the sun.
