GEOGRAPHY. 



timp, and which he had aftunlly in his pcfTeffion. Thefe 

 conliilcd of various particulars, lome of greater and others 

 of a lofs degree of authenticity. Tiie principal were the 

 " proportions of the gnomon" toils fliadow, taken by dif- 

 ferent ntlronomers at tiie times of the equinoxes and lolllices ; 

 " calculations" founded upon the length of thelongeft days ; 

 "the meafurcs" or computed diflances of the principal 

 roads contained in their furvcys and itineraries, and the 

 various " reports of travellers and navigators," who often 

 determinec^ the intervals of places by hear-fay and guefs- 

 v.crk. All of thefe were to be compared together, and 

 digefted into one uniform body or fyilem, and after this, were 

 converted and tra:!l1atedby him into a new mathematical lan- 

 guage, expreffing their different degi-ees and minutes of 

 litltude and longitud-, according to the invention of Hippar- 

 chus, but which Ptolemy had the merit of carrying into 

 full prafticc and execution, after it had been neglefted for 

 upwards of 250 years. We have no reafon to fuppofe, that 

 Piolemy had in his poirelTion real aftronomical obfervations 

 fufficient to determine all the longitudes and latitudes which 

 he has given ; fo that we ought always to remember, that 

 their degrees of accuracy depended upon the vei-acity of the 

 faCl or fuggeftion communicated to him, from which they 

 were afterwards deduced. We have therefore no reafon to 

 be alloniflied at the multitude of errors that are to be found 

 in it, when his original materials were fo imperfeft for exe- 

 cuting fo large a work, as that of fixing the longitudes and 

 latitudes of all the places, coails, bays, and rivers of the then 

 knov/n world ; an undertaking which, even in our days, 

 has not hitherto been brought to any fufficient degree of ac- 

 curacy. The miftakes of Ptolemy ought to be regarded 

 with candour, as they arofe from th.e ignorance of the age 

 in which he lived, which could give him no better informa- 

 tion, and not from ignorance or inattention en his own part. 

 Nevcrthelefi, Ricciolus, Cellarius, Paul Merula, and Sal- 

 mafms have been too fevere in their criticifm and cenfures ; 

 :<s if they were difappointed in not feeing this fcience in its 

 full maturity in the writings of Ptolemy, at a time when it 

 was evidently but juft beginning to advance beyond the verge 

 of its earheil infancy. They might with equal juftice con- 

 demn the modern geographers for giving no better account 

 of Nova Zembla, or New Holland, or of thofe continents 

 and iflands that lie on the northern or foutliem extremities of 

 the great South fea towards the tvi'o Poles ; of which the 

 knowledge which they could obtain was very imperfeft. 

 The principal millakes in Ptolemy took their rife from cer- 

 tain aih-onomical obfervations and furveys, which were fup- 

 pofed to have been made with accuracy in a prior age, and 

 which v>'ere adopted by this great geographer as genuine ; 

 ;ind they have been, for want of better information, copied 

 by fucceeding geographei'S and inferted ui their maps, as 

 being, in their opinion, of acknowledged and undoubted 

 authority. Thefe miftakes, thus introduced, maintained 

 tlieir places in all maps, by a kind of unqueftioned prefcrip- 

 tion, even to the commencement of the lail century, audit 

 unfortunately happened that thefe errors related to that part 

 of the world which was beil known to the ancient Greeks and 

 Romans. Thus, Ptolemy ftates the latitude of Byzantium 

 to be 43' 5' inftead of 41 l', the latitude according to mo- 

 dern obfervations. In this particular Ptolemy was milled 

 fiy Hipparchus, who is mentioned by Strabo (1. i.) as 

 luving vifited Byzantium, and made this obfervation in 

 perfon. Th-' latitude of Marfeilles, which was fuppofed to 

 be under the fame parallel witii Byzantium, was not, however, 

 fo much miftaken, as by modern obfervations it has been 

 found to be 43 ' 17' 45"; and allowance being made for the 

 now acknotilcdged diminution of the obliquity of the 



ecliptic, (fee Ecliptic,) the refult will be nearer the truth. 

 Another error of Ptolemy relates to the latitude of ancient 

 Carthage, which he has placed in 32" 20' inftead of 36 52', 

 the true latitude according to the beft obfervations. This 

 erroneous latitude feems to have been copied or tranflated 

 from a pafiage in Strabo (1. ii.), in which it is ft^ited that 

 at Carthage the gnomon has the fame proportion to tke 

 equinoftial fnadow, which li has to 17, whence by plain 

 trigonometry v%e {liall have the latitude of 32- 2Sj', very 

 near that of Ptolemy. The third capital miftake of Ptolemy 

 relates to the length of the Mediterranean, which is generally 

 meafured from the ftraits of Gibraltar to the bottom of the 

 bay of Iftus, where Alexandretta, or Scanderoon, now 

 ftands, whole ancient name was Alexandria ad KFum. The 

 difference of longitude of Alexandria ad Ifliim and Gibraltar, 

 according to Ptolemy, is 62 o' ; whereas the difference of 

 longitude between thefe two places, according to the lateft 

 obfervations, is 41- 28, and Ptolemy's error is 20° 32'. 

 This error, which continued in all our maps, more or lefs, 

 till the beginning of the laft century, took its rife from the 

 fuppofed furveys of perfons of reputation, recorded by 

 Strabo. (See Degree, Earth, and Longitude.) But 

 to return from this digreffion : — many valuable geographical 

 works appeared under Dioclehan, Conilantius, and 

 Maximian, &c. Under the emperor Theodofius the pro- 

 vincial and itinerary chart or table, fince known under the 

 name of Peutinger, was digefted and formed ; and the laft 

 work, that ought to be claffed with thofe of the ancients^ 

 was the Notitia Imperii, attributed to jEthicus, v.-ho lived 

 between the years 400 and 450 of the Chriftian era. The 

 ages of barbarifm fucceeded the fall of the Roman empire ;. 

 and the arts and fciences were obliged to feek refuge and pro- 

 tettion from the Arabians and Orientalifts in Aila ; tlie 

 principal of whom, diilinguifhed by their attention to geo- 

 graphy, were Almamom, cahph of Babylon, and AbuLfeda,. 

 a Syrian prince. (See Degree.) After the revival of 

 learning in Europe, and particularly during the two laft cen- 

 turies, geography has derived very confiderable accefiions 

 from travels, voyages, and a variety of nautical and aftro- 

 nomical obfervations. 



The great misfortune of ancient geography, and which 

 indeed confined it to fuch a lingering ftate of infancy, \vas,. 

 that the true method of determining with accuracy the dif- 

 ference of longitudes was a matter of fuch difficulty, and 

 remained fo long unknown. One of the firft attempts to 

 reftify the length of the Mediterranean was made under the 

 aufpices of M. de Peirefli in 1635 ; and he alfo, with a di- 

 rect view of correfting the errors in the longitudes of dif- 

 ferent places, took particular pains to get obfervations made 

 at Marfeilles, Aleppo, and Grand Cairo, of an eclipfe of 

 the moon, which happened Auguft the 27th 1635. Before 

 that time the difference of longitude between Marfeilles and 

 Aleppo had been fuppofed to be 45 ', but by thefe obfer- 

 vations it was found only to amount to 30' (the real differ- 

 ence has been iince found to be 31^ 58 ) ; fo that by this a 

 very confiderable correftion was made in the length of the 

 Mediterranean, by taking off the difference of one whole 

 hour, or ij', at once. About this time eclipfes of the fun 

 and moon were thought fufficient to determine the longitudes 

 of all places with a tolerable accuracy. But, in the event, 

 the ableil aftronomers foon found that from thefe eclipfes, 

 however carefully obferved, no clear deduction could be 

 made of the longitude of any one place to any fuincient de- 

 gree of exaftnefs. Honce feveral eminent aftronomers, 

 inch as Fournier, Kircher, and even Ricciolus, who had 

 colleftcd the obfervations of no lefs than 56 eclipfes of the 

 fun and moon, between the years ij6o and 1658, gave up 



the 



