e other that hath any certainty of observati[~o] in
it. That by Eclipses is most vncertain, for a little error in a
few minuts of time (which the observers shall not possibly
avoide) breeds a sensible and fowle error in the distance of the
two places of observation. That of _Eratosthenes_ by the Sunne
beames, and a shadow of a stile or gnomon set vpon the Earth, is
as bad as the other. For both the vncertainty of the calculation
in so small quantity as the shadow and the gnomon must needs
haue, and the difficulty to obserue the true length of the
shadow, as also the false supposition wherevpon it proceeds,
taking those lines for Paralells which are not, doe manifestly
shew the reckoning hereby made to be doubt full and not sure.

2 The second is by measuring the semidiameter of the Earth: For
as the circumference makes knowne the diameter, so doth this the
circumference. This may be done by observation made vpon some
great hill, hard by the sea side. The invention is of _Maurolycus
Abbot_ of _Messava_ in _Sicilie_, but it hath beene perfitted,
and more exactly performed by a worthy Mathematician _Ed. W._ who
himselfe made proofe of it. By this art was the semidiameter of
the Earth found out to be 18312621 foote: which allowing 5000
foot to a mile is 3662 & a halfe miles, which doubled is the
whole Diameter 7325 miles. The circuit of the earth shall be
23030 miles, and one degree containes 63-35/36 miles which is
almost 64 miles. Which as it exceeds the ordinary account, so may
wee rest vpon it as more exact then any other.

2 The second point concerninge the measuringe of particular
distances of places one from another is thus performed.

First vpon the Globe it is most easie. With a payre of Compasses
take the distance betweene any two places howsoever scituated
vpon the Globe, and apply the distance so taken to the AEquator, &
see how many degrees it takes vp; those degrees turned into miles
shew the distance of the two citties on from another.

Vpon vniuersall mapps theire is a little more difficulty in
finding the distance of places which here must bee considered in
a threefold difference of scituation:

1 Of Latitude only.

2 Of Longitude only.

3 Of Latitude and Longitude together.

1 If the two places differ only in Latitude, and lie vnder the
same Meridian if the places lie both on one side of the AEquator,
the differences of the latitudes: or the summe of both latitudes
added together, i