Its object is to enable a traveller to use the sun, both as a rude watch
and as a compass. The diagram is calculated for the latitude of London,
but will do with more or less accuracy for the whole of England. A
traveller going to other countries may easily draw up one for himself,
and on a larger scale if he prefers it, by using the Azimuth tables and
the Horary tables of Lynn.
The diagram represents, 1st, circles of equal altitudes; 2ndly, the path
of sun, stars, etc., for each 10th degree of declination; 3rdly, the hour
angles, all projected down upon--4thly--the level compass card.
Thus, six circles are drawn round the centre of the compass card at equal
distances apart, each ring between them representing a space of 15
degrees in altitude.
The following angles were then calculated for each 10th degree of
declination in turns, viz.:--The height of the sun, etc., when above the
horizon at each point of the compass. 2ndly, the bearing of the sun at
each consecutive hour. These points were dotted out; and, by joining the
several sets of them, the drawing was made.
The broken lines which diverge in curves from P are hour lines; those
which surround P in more or less complete ovals, are the paths of the sun
and stars, for each 10th degree of declination; the prominent line
running from E. round to W. being its path when on the Equator.
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