month may be deduced from the declination of the sun; and,
to obtain the latter, all the data required are,

1. The latitude of the place.

2. Two altitudes of the sun at different sides of noon.

It is not absolutely necessary to have any previous knowledge of the hours
at which these altitudes were respectively obtained, because these may be
discovered by the trial method of seeking two such hours as shall most
nearly agree in requiring a declination common to both at the known
altitudes. Of course it will greatly simplify the process if we furthermore
know that the observations must have been obtained at some determinate
intervals of time, such, for example, as complete hours.

Now, in the Prologue to the "Canterbury Tales" we know that the
observations could not have been recorded except at complete hours, because
the construction of the metre will not admit the supposition of any parts
of hours having been expressed.

We are also satisfied that there can be no mistake in the altitudes,
because nothing can alter the facts, that an equality between the length of
the shadow and the height of the substance can only subsist at an altitude
of 45 degrees; or that an altitude of 29 degrees (more or less) is the
nearest that will give the ratio of 11 to 6 between the shadow and its
gnomon.

{386}

With these data we proceed to the following comparison:

_Forenoon altitude_ 45deg.|| _Afternoon altitude_ 29deg.
||
Hour. Declin. || Hour. Declin.
XI A.M. 8deg 9' N. || II P.M. 3deg 57' S.
X " 13deg 27' " || III " 3deg 16' N.
IX " 22deg 34' " || IV " 13deg 26' "
VIII " Impossible. || V " Impossible.

Here we immediately select "X A.M." and "IV P.M." as the only two items at
all approaching to similarity; while, in these the approach is so near that
they differ by only a single minute of a degree!

More conclusive evidence therefore could scarcely exist that these were the
hours intended to be recorded by Chaucer, and that the sun's declination,
designed by him, was somewhere about thirteen degrees and a half North.

Strictly speaking, this declination would more properly apply to the 17th
of April, in Chaucer's time, than to the 18th; but since he does not
profess to critical exactness, and since it is always better to adhere to
written authority, when it is not grossly and obviously corrupt,