AMONG the several improvements made in arts and sciences by ingenious
men, the construction of _globes_, _maps_, or _charts_, deserves a
place: not only on account of the pleasure and satisfaction that
arises to speculative minds, in surveying the extent and divisions of
this terraqueous globe, but also for their real use and service to
navigation, trade, and commerce.
_Globes_ perhaps were first invented, as bearing the nearest semblance
to the natural form of the earth and sea, with proper circles thereon
described, and the several empires and kingdoms, according to their
extent, latitudes, and longitudes, as far as geography and history
would admit.
But tho’ these convey the most general and truest ideas of the position
and situation of places; yet, as containing but a small surface, they
were found not extensive enough to take in particular kingdoms or
states, with their subdivisions, cities, and rivers, so as to convey
an adequate and sufficient representation. Besides, they were not so
portable and commodious in voyages or travels.
_Maps_ and _Charts_ were therefore thought of, as being most convenient
for both the purposes above-mentioned; the accuracy of which depends
on representing the meridians and parallels in such manner, that when
places are laid thereon, according to their latitudes and longitudes,
they may have such respect to each other, as they have on the globe
itself; and those are either _globular_ or _rectilinear_.
_Globular_, or _curvilinear_, are either general or particular.
_General_, are the hemispheres; for the most part constructed
stereographically.
_Particular_, contain only some part of the terraqueous globe; and of
this sort there are sundry modes of construction, which for the most
part are defective, so as not to be applied with accuracy and facility
to the purposes intended, in determining the courses or bearings of
places, their distances, or both.
_Rectilinear_ were therefore very early adopted, on which the meridians
were described parallel to each other, and the degrees of latitude and
longitude every-where equal; the rumbs were consequently right lines;
and hereby it was thought, that the courses or bearings of places would
be more easily determined.
But these were found also insufficient and erroneous, the meridians
being parallel, which ought to converge; and no method or device used
to accommodate that parallelism.
Notwithstanding the great deficiency in this plane map or chart, it was
preferred, especially in nautical business; and hath its uses at this
day in topographic constructions, as in bays, harbours, and very narrow
zones.
However, the errors herein were sooner discovered than corrected, both
by mathematicians and mariners, as by Martin Cortese, Petrus Nonius,
Coigniet, and some say by Ptolemy himself.
The first step towards the improvement of this chart was made by
Gerardus Mercator, who published a map about the year 1550, wherein the
degrees of latitude were increased from the equator towards each pole;
but upon what principles this was constructed, he did not exhibit.
About the year 1590, Mr. Edward Wright, an Englishman, discovered
the true principles upon which such a chart should be constructed;
and communicated the same to one Jodocus Hondius, an engraver, who,
contrary to his honest faith and engagement, published the same as
his own invention: This occasioned Mr. Wright, in the year 1599, to
exhibit his method of construction, in his book, intitled, _Correction
of Errors in Navigation_; in the preface of which book may be seen
his charge and proof against Hondius; and also how far Mercator has
any right to share in the honour due for this great improvement in
geography and navigation.
Blundevill, in his Exercises, page 327, published anno 1594, gives a
table of meridional parts answering to even degrees, from 1° to 80°
of latitude, with the sketch of a chart constructed therefrom; but
this table he acknowledged to have received from Mr. Wright, in the
following words, page 326, _viz._ “In the mean time to reform the saide
faults,” (in the plane chart) “Mercator hath in his universal chard or
mappe made the spaces of the parallels of latitude to bee wider everie
one than other from the equinoctial towards either of the poles, by
what rule I know not, unless it be by such a table as my friend Maister
Wright of Caius-college in Cambridge at my request sent me (I thank
him) not long since for that purpose, which table with his consent, I
have plainlie set down,” _&c._
About the year 1720, a globular chart was published, said to be
constructed by Mr. Henry Wilson; the errors in which were obviated
by Mr. Thomas Haselden, in a letter to Dr. Halley; who at the same
time exhibited a new scale, whereby distances on a given course may
be measured, or laid off, at one extent of the compasses, on Wright’s
projection; and was intended to render the same as easy in practice as
the plane chart.
The above chart was published in opposition to Mr. Wright’s, which that
author charged with imperfections and errors, and that it represented
places bigger than they are upon the globe.
It is true, the surface is apparently enlarged; but the position of
places, in respect to one another, are in no wise distorted; and it may
be asserted, with the same parity of reason, that the lines of sines,
tangents, and secants, are false, because the degrees of the circle,
which are equal among themselves, are thereupon represented unequal.
Yet if a map or chart was so constructed, as to shew the situation and
true extent of countries, _&c. primâ facie_ (if I may be allowed the
expression), and yet retain all the properties, uses, and simplicity,
of Wright’s construction, it would be a truly great improvement; but
this seems to be impossible.
The method exhibited by the Rev. Mr. Murdoch, in his paper, read before
the Royal Society on the 9th of February last, shews the situation of
places, and seems better calculated for determining superficial and
linear measures, than any other that has occurred to me.
This Gentleman illustrates his theory with examples justly intended to
point out the quantity of error, that will happen in a large extent.
For instance; Between latitudes 10° and 60° N. and containing 110
degrees difference of longitude, Mr. Murdoch computes the distance at
5594 miles; which, upon the arc of a great circle, is found to be 5477,
or by other methods 5462; so that the difference is only 117, or at
most 132 miles in so great an extent, and to an high latitude; and the
higher the latitude the greater the error is like to be, where-ever
middle latitude is concerned.
His courses also agree very nearly with computations made from the
tables of meridional parts.
In example the first they are the very same:
In example the 2d they agree to half a minute:
In example the 3d they vary 1° 4´, on account of the high latitudes,
which extend from 56° to 80° N.
However, I do not esteem this method so simple, easy, and concise, in
the practice of navigation, as Mr. Wright’s construction, especially in
determining the bearings or courses from place to place: nor will it (I
presume) admit of a zone containing both north and south latitude.
Of these inconveniences Mr. Murdoch seems to be extremely well
acquainted, when he expresses himself in the following very candid and
ingenuous terms, _viz._ “As to Wright’s or Mercator’s nautical chart,
it does not here fall under our consideration: it is perfect in its
kind; and will always be reckoned among the chief inventions of the
last age. If it has been misunderstood or misapplied by geographers,
they only are to blame.”--And again, at the end of his nautical
examples, he concludes thus, _viz._ “It is not meant, however, that it
ought to take place of the easier and better computation by a table of
meridional parts.”