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MARITIME AND INLAND DISCOVERY.
PROGRESS OF GEOGRAPHICAL SCIENCE.
Geographical Science in the Middle Ages. ---Errors of Antiquity adopted by the
Learned.---Supposed Longitudes of Nuremberg and Rome; of Ferrara and Cadiz.--- Improvements in Maps.---Doubtfulness respecting the Distance and Separation of Asia and America.-Galileo.--Eclipses of Jupiter's Satellites employed to find the Longitude.--Observations of Picard. The Map of France reformed. --Labours of Cassini.---Chazelles rectifies the Map of the Mediterranean.---Geography reformed by Delisle.---Peter the Great visits him.-D'Anville.--Influence of Newton.-Halley.His Voyage to St. Helena.-He invites the Attention of the Learned to the Transit of Venus. Studies Physical Geography.--Improves the Theory of Lunar Motions.-Belief in the Existence of a Southern Continent.--Dalrymple.-His Plans of Colonization, and Code of Laws.
THE various branches of human knowledge are so intimately interwoven, that it is hard to conceive an improvement in one which does not conduce to the advantage of the others. The modes of connection which exist between the numerous objects of mental research, are, like the membranes that embrace the humours of the eye, so minute and transparent, that while they give union and solidity to the whole, they themselves remain unperceived, or wholly invisible. The general advancement in knowledge which followed the discovery of the art of printing, and the increased activity and spirit of mercantile enterprise resulting from the discoveries of Columbus and Vasco de Gama, all seemed to conspire to the improvement of geography; and one might have supposed that this study would have been the first to arrive at perfection: but notwithstanding the zeal with which geographical inquiries were prosecuted during the sixteenth century, this science grew up with so many original imperfections, that its rudeness and deformity, compared with its sister sciences, became continually more conspicuous. .
No errors are so difficult to correct as those which are adopted by the people. Opinions received implicitly are seldom overturned by the arguments of reason; thus geography laboured under a disadvantage from the very popularity of its nature. A system was in vogue, and, though manifestly incorrect, still maintained its ground until the scientific principles against which it offended became as generally known and recognized. The most eminent geographers of the 16th and 17th centuries were men of learning, who, in the spirit of that age, adopted with zeal and obstinacy all the mistakes committed by the writers of antiquity. The authority of their names, added to that of the ancient writers on whom they rested, offered an inert resistance which scientific geographers were long unable to overcome.
The first requisite in a correct system of geography is, to determine accurately the relative position of places; but in this the ancients were guilty of gross errors. The method which they employed to determine the latitude of places admitted of but little precision, and their determination of longitude was stijl more erroneous
The countries with which the Greek and Roman writers were best acquainted were those situated on the shores of the Mediterranean Sea ; and here, of course, we should expect to find their geographical accuracy exhibited to advantage:yet Constantinople or Byzantium, the capital of the eastern empire, is placed by Ptolemy two degrees to the north of its true position. The Arab writers, who seem to have learned that there was an error of two degrees, without knowing in which direction instead of lessening the latitude of Constantinople from 43 to 41, which would have been near the truth, increased it to 45, thus placing that city in their maps 276 English miles to the north of its true place. When Amurath III., about 1580, caused observations to be made, which reduced the latitude of that city to 41° 30 the learned were indignant that barbarians should think of correcting Hipparchus.
As the northern shore of the Mediterranean was placed by Ptolemy in general too far to the north, so the southern shore was removed too far to the south; the breadth of that sea being thus increased far beyond the truth. The latitude assigned to Carthage was 32° 20, which is 4° 32' or 313 English miles to the south of its true place. This gross error was not taken notice of till 1625. .
But these errors of the ancients in calculating latitudes were far exceeded by those which they committed in measuring the longitude, even at the places with which they were best acquainted. The length of the Mediterranean from Calpe or Gibraltar to the bottom of the bay of Issus, where Scanderoon stands at present, which is really a distance of 41° 28, is increased in the map of Ptolemy to 62 degrees. Thus the error in the length of the Mediterranean alone amounts to 20° 32, or nearly 1400 English miles; and this enormous error continued in the maps of Europe with little change till the beginning of the last century:
The difficulties of ascertaining the longitudes of places while astronomical observations were still deficient in precision, and the extent to which those errors were carried during the middle ages in fixing the relative positions of even the best known places of Europe, may be estimated from the following list, formed by Kepler, who, feeling that his own observations would overturn those of antiquity, pleaded by way of excuse the inevitable uncertainty of these calculations :
The difference in longitude between Rome and Nuremberg in the time of
Regiomontanus was reckoned at · go
- 8 15
- 4 Apianus again
- 4 45
- 6 30
Kepler T'hus the difference in longitude between two of the best known towns in Europe varied above 500 miles from the fifteenth to the seventeenth centuries. But this uncertainty will appear more remarkable when found to exist in the longitudes of places which are nearly in the same latitude. For this purpose Ferrara and Cadiz may be conveniently compared. The difference of the longitude between these two places as stated by
Ptolemy in the edition of 1475 was 27° 20
. 1638 Riccioli
1677 De Lalande . . .1789
Hence it appears, that in the maps of the sixteenth century Cadiz and Ferrara were placed 600 miles too far asunder, and that this egregious error still maintained its ground till the close of the seventeenth century.*
Errors of a wilder kind, originating rather in credulity than in positive inaccurate observation, found a place in the maps of the middle ages, and were tardily banished from them, at a comparatively recent date, by the improvements of astronomy and navigation. We will here glean a few of those errors from the best of the early maps..
From a map of the world published in Venice in 1546, by Giacomo, we find Asia and America united in lat. 38o. Thibet is placed at the junction of the two continents, and Zangar is the name given to the remote region on their frontiers. California, it is remarkable, is here described as a peninsula. China, conformably to the map of Ptolemy, stretches to the 180th degree. In the South Sea the Isla de los Tuburones, discovered by the Spaniards, is marked in 10° S. lat.
In another Venetian map by Tramezini, dated 1554, the distance from Quinsai in China to the gulf of California in Amer. ica is only 31°;—these two continents being unduly stretched some thousand miles respectively to the east and west. In this map is marked the Island of Papuas, or New Guinea, and the Ladrones; but it is remarkable that Asia and America are here separated by a wide strait, the author observing in a note, “In this place we have followed the latest authorities in separating this coast of Tartary from the continent of America." He thus insinuates that his delineation of the shores round the Pacific was founded on something better than mere caprice. Yet in the Venetian maps which immediately followed, the two continents are again united. In all these maps we find the Terra Australis adhuc inexplorata, or southern land, as yet unexplored; and the first printed map in which more positive indications occur in this quarter appears to be that executed by Fernando Bartoli in 1571. In this we find the Terra incognita discrioperta di Nuovo, or lately discovered, situated to the south of New Guinea and the Spice Islands, or corresponding with the general situation of New Holland. In this, as in other early maps, the Terra Australis is represented as one great continent, filling the antarctic regions ; but Bartoli has named some portions of it as if he had received information of land in those directions. Thus, to the south of the Cape of Good Hope is a promontory named Terra de Vista.
Notwithstanding the great increase of geographical information, even the best maps were long deficient in correct dis
* See a dissertation on the fluctuation of longitudes in the middle ages, by Canovai, in the Memorie dell' Academia di Cortona, vol. ix.
tances, particularly in longitude. South America is represented by Fischer as 62 degrees, or near 4500 miles across; while North America, in the same map, extends from the mouth of the St. Lawrence on the east, to New Albion on the west, through a space of 150 degrees, or above 9000 miles. Here also we find California again represented as an island, an error which is repeated in many maps executed at the commencement of the eighteenth century; and in some of them the northwest coast of America is represented as running westward in the parallel of 42°, till it nearly meets Yedzo; it is 'then marked as doubtful. It is remarkable that in some of these maps we find the south coast of New Guinea delineated, though at a later period that island was supposed to be connected with New Holland. The Terra Australis, or antarctic continent, which De Witt banished from his maps, was restored by Sanson in the beginning of the last century; so slow and fluctuating was the progress of accurate geography. Hondius, in 1630, ventured to abridge Asia of the undue dimensions given to it by Ptolemy, and to reduce its extension towards the east to 165°. But his example was not followed, and many instances might be adduced in which the authority of Ptolemy, who was but slightly acquainted with one half of the globe, was blindly submitted to in an age when Europeans wandered over its entire surface.
As scientific knowledge advanced, hopes were entertained that the longitudes of places might be fixed by observing the eclipses of the sun and moon; but this method proved, on experience, to be so pregnant with error that astronomers were again reduced to despair. A grand step, however, was made towards the attainment of their wishes, when in 1610 Galileo discovered the eclipses of Jupiter's satellites. In 1631 that great man proposed to the king of Spain to apply his discoveries for the purposes of navigation and geography. The supineness of the Spanish court was not calculated to foster his zeal; but the Dutch embraced his offer, and sent Hortensius and Blaew to study under him at Florence. Yet the defects of telescopes, and the mistakes of his followers, long stood in the way of that improvement which must otherwise have been the immediate consequences of Galileo's discoveries. At a time when some astronomers imagined that they saw no fewer than twelve satellites round Jupiter, no satisfactory conclusions could be drawn from the observation of that planet. Until Cassini published his tables in 1668 nothing accurate was known respecting the eclipses and revolutions of Jupiter's satellites. Shortly afterwards, however, in 1671,) Picard went to Uraniburg in Denmark, to the observatory of Tycho Brahe, to observe according to the advice of Cassini. He was thus able to calculate,