Geographical Definitions.
_Of the Situations of Places upon the Earth; of the
different Situations of its Inhabitants; of Zones
and Climates._
The situations of places upon the Earth, are determined by their
Latitude and Longitude.
[Sidenote: _Latitude._]
1. The _Latitude_ of any place (upon the Earth) is its nearest
distance, either North or South from the Equator; and if the place
be in the (Northern/Southern) hemisphere, it is accordingly called
(_North_/_South_) _Latitude_; and is measured by an arch of the
meridian intercepted betwixt the zenith of the said place, and the
equator. And all places that lie on the same side, and at the same
distance from the equator, are said to be in the same parallel of
latitude: the parallels in _Geography_, being the same with the
parallels of declination in _Astronomy_.
From this definition arise the following Corollaries.
(1.) _That no place can have above 90 degrees of latitude,
either North or South._
(2.) _Those places that lie under the equinoctial (or
thro’ which the equator passes) have no latitude, it being
from thence that the calculation of latitudes is counted;
and those places that lie under the Poles have the greatest
latitude, those points being at the greatest distance from
the equator._
(3.) _The latitude of any place is always equal to the
elevation of the Pole in the same place above the horizon;
and is therefore often expressed by the Pole’s height, or
elevation of the Pole; the reason of which is, because from
the equator to the Pole there is always the distance of 90
degrees, and from the zenith to the horizon the same number
of degrees, each of these including the distance from the
zenith to the Pole: That distance therefore being taken
away from both, will leave the distance from the zenith to
the equator, (which is the latitude) equal to the distance
of the Pole to the horizon._
(4.) _The elevation of the equator in any place is always
equal to the complement of the latitude of the same place._
(5.) _A ship sailed directly (towards/from) the equator
(lessens/augments) her latitude, (or (depresses/raises) the
Pole) just so much as is her distance sailed._
[Sidenote: _Difference of Latitude._]
2. _Difference of latitude_ is the nearest distance betwixt any two
parallels of latitude, shewing how far the one is to the Northward or
Southward of the other, which can never exceed 180 degrees. And when
the two places are in the same hemisphere (or on the same side of the
equator) the lesser latitude subtracted from the greater, and when they
are on different sides of the equator, the two latitudes added, gives
the difference of latitude.
[Sidenote: _Longitude._]
3. The _Longitude_ of any place (upon the Earth) is an arch of the
equator, contained betwixt the meridian of the given place, and some
fixed or known meridian; or, it is equal to the angle formed by the two
meridians, which properly can never exceed 180 degrees, tho’ sometimes
the Longitude is counted Easterly quite round the globe.
Since the meridians are all moveable, and not one that can be fixed
in the heavens, (as the equinoctial circle is fixed, from whence the
latitudes of all places are determined to be so much either North or
South) the longitudes of places cannot so well be fixed from any other
meridian, but every Geographer is at his liberty to make which he
pleases his first meridian, from whence to calculate the longitudes
of other places. Hence it is that geographers of different nations
reckon their longitudes from different meridians, commonly choosing the
meridian passing through the metropolis of their own country for their
first: Thus, the _English_ geographers generally make the meridian of
_London_ to be their first, the _French_ that of _Paris_, and the
_Dutch_ that of _Amsterdam_, &c. and mariners generally reckon the
longitude from the last known land they saw. This arbitrary way of
reckoning the longitude from different places, makes it necessary,
whenever we express the longitude of any place, that the place from
whence it is counted be also expressed.
From the preceding definitions arise the following corollaries:
1. _If a body should steer directly North, or
directly South, quite round the globe, he’ll
continually change his latitude; and pass through the
two Poles of the world, without deviating the least
from the meridian of the place he departed from; and
consequently on his return will not differ in his
account of time from the people residing in the said
place._
2. _If a body should steer round the globe either
due East, or due West, he’ll continually change his
longitude, but will go quite round without altering his
latitude; and if his course should be due East, he’ll
gain a day compleatly in his reckoning, or reckon one
day more than the inhabitants of the place from whence
he departed; or if his course had been West, he would
have lost one day, or reckon one less._
The reason of which is evident; for admitting our traveller steers due
East; so many miles in one day as to make his difference of longitude
equivalent to a quarter of an hour of time, it is evident that the
next day the Sun will rise to him a quarter of an hour sooner than to
the inhabitants of the place from whence he departed; and so daily,
in proportion to the rate he travels, which in going quite round,
will make up one natural day. In like manner, if he steers due West
after the same rate, he’ll lengthen each day a quarter of an hour,
and consequently the Sun will rise to him so much later every day; by
which means, in going quite round, he’ll lose one day compleat in his
reckoning. From whence it follows,
3. _If two bodies should set out from the same place,
one steering East, and the other West, and so continue
their courses quite round, until they arrive at the
place from whence they set out, they’ll differ two days
in their reckoning at the time of their return._
4. _If a body should steer upon an oblique course (or
any where betwixt the meridian and the East or West
points) he’ll continually change both latitude and
longitude, and that more or less, according to the
course he steers; and if he should go quite round the
globe, he’ll differ in his account of time, as by the
second Corol._
5. _The people residing in the Easternmost of any
two places, will reckon their time so much the sooner
than those who live in the other place, according to
the difference of longitude betwixt the two places,
allowing one hour for every 15 degrees, &c. and the
contrary._