It Would Be Almost Endless To
Enumerate Those To Whom Modern Geography, And The Construction Of Modern
Maps Are Principally Indebted.
Gaspari and Zimmerman, among the Germans,
have thrown into a philosophical and interesting form the labours and heavy
details
Which were supplied them by less original but more plodding men.
The English, though, as Malte Brun observes, they are still without a
system of geography which deserves the name, are rich in excellent
materials, which have been supplied by the extent of their dominions and
their commerce in various parts of the globe; by their laudable and happy
union of conquest, commerce, and science; and by the advantage which
Dalrymple, Arrowsmith, and other geographers have derived from these
circumstances. The French, Russians, Spaniards, Danes, and indeed most
nations of Europe, sensible of the vast importance of accurate maps,
especially such as relate to their respective territories, have contributed
to render them much more accurate than they formerly were; so that at
present there is scarcely any part of the globe, which has been visited by
sea or land, of-which we do not possess accurate maps; and no sooner has
the labour of any traveller filled up a void, or corrected an error, than
the map of the country which he has visited becomes more full and accurate.
The most direct and perfect application of mathematical and astronomical
science to the delineation of the surface of the globe, so as to ascertain
its exact form, and the exact extent of degrees of latitude in different
parts of it, has been made by the English and French; and much to their
honour, by them in conjunction. The first modern measurement of degrees of
latitude was made by an Englishman of the name of Norwood: he ascertained
the difference of latitude between London and York in 1635, and then
measured their distance: from these premises he calculated, that the length
of a degree was 122,399 English yards. At this time there was no reason to
suppose that the earth was flattened at the Poles. Shortly afterwards, it
having been discovered that the weights of bodies were less at the equator
than at Paris, Huygens and Cassini directed their attention, as we have
already stated, to the subject of the figure of the earth. In 1670 Picard
measured an arc of the meridian in France; and in 1718, the whole area
extending through France was measured by Cassini and other philosophers.
The results of this measurement seemed to disprove Newton's theory, that
the curvature of the earth diminished as we recede from the equator. To
remove all doubts, an arc near the equator was measured in Peru, by some
French and Spanish astronomers; and an arc near the arctic circle by some
French and Swedish astronomers; the result was a confirmation of Newton's
theory, and that the equatorial diameter exceeded the polar by about 1/204
part of the whole.
Since this period, arcs of the meridian have been measured in several
countries. In 1787 it was determined by the British and French governments
to connect the observatories of Greenwich and Paris by a series of
triangles, and to compare the differences of latitudes and longitudes,
ascertained by astronomical observations, with those ascertained by actual
measurement. The measurement in England was extended to a survey of the
whole kingdom; and the accurate maps thus obtained have been since
published. Arcs of the meridian have also been measured lately from Dunkirk
to Barcelona, - in Lapland, by which an error in the former measurement
there was corrected; - and in India.
We have been thus particular in our notice of this subject, because it is
evident that such measurements must lie at the foundation of all real
improvements in the construction of maps.
Let us next turn our attention to the improvements in navigation which have
taken place during the last and present centuries; these seem to consist,
principally, in those which are derived from physical science, and those
which are derived from other sources.
The grand objects of a navigator are the accurate knowledge of where he
exactly is, in any part of his course, and how he ought to steer, in order
to reach his destination in the shortest time. The means of ascertaining
his latitude and longitude, of calculating how far he has sailed, and at
what rate he is sailing, and the direction of his course with reference to
the port to which he is desirous to proceed, are what he principally
requires. We do not intend, by any means, to enter at any length, or
systematically, on these subjects; but a brief and popular notice of them
seems proper and necessary in such a work as this.
Astronomy here comes essentially to the aid of navigation: we have already
seen how, even in the rudest state of the latter, it derived its chief
assistance from this sublime science, confined as it then was to a
knowledge of the position of a few stars. Astronomy enables the navigator
to ascertain his latitude and longitude, and to find the variation of the
compass. The principal difficulty in ascertaining the latitude at sea,
arose from the unsteady motion of the ship: to remedy this, several
instruments were invented. We have already alluded to the astrolobe; but
this, as well as the others, were imperfect and objectionable, till such
time as Hadley's quadrant was invented, the principle and uses of which
were first suggested by Newton.
To ascertain the longitude was a much more difficult task: there are
evidently two methods of doing this, - by time-keepers or chronometers, and
by making the motions of the celestial bodies serve instead of
time-keepers. About the middle of the seventeenth century, Huygens proposed
the pendulum clock for finding the longitude at sea; but it was unfit for
the purpose, for many and obvious reasons. Watches, even made with the
utmost care, were found to be too irregular in their rate of going, to be
depended upon for this purpose.
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