A Dictionary of Greek and Roman biography and mythology. By various writers. Ed. by William Smith. Illustrated by numerous engravings on wood.

PTOLEMAEUS. PTOLEMAEUS. 579
straight lines which converge, north of the equator, south; a circumstance natural enough, since the
towards the common centre of the arcs which repre- methods of taking latitudes with tolerable precision
sents the parallels of latitude; and, south of it, to- had long been known, and he was very carefill to
wards a corresponding points representing the South avail himself of every recorded observation which
Pole. Having laid down these lines, he proceeds he could discover. But his longitudes are very
to show how to give to them a curved form, so as wide of the truth, his length of the known world,
to make them a truer representation of-the meri- from east to west, being much too great. The
dians on the globe itself. The portion of the sur- westernmost of the Canaries is in a little more than
face of the earth thus delineated is, in length, awhole 180 W. long., so that Ptolemy's easternmost merihemisphere, and, in breadth, the part which lies dian (which, as just stated, is in 1100 or 1200 E.
between 630 of north latitude and 1 63~O of south long.) ought to have been that of 128 or 1 380,
latitude. or in round numbers 1300 or 1400, instead of 1800;
2. Thle Historical or Positive Geographty of Pto- a difference of 500 or 400, that is, from 1-7th to
lemy.-The limits just mentioned, as those within 1-9th of the earth's circumference.
which Ptolemy's projection of the sphere was con- It is well worthy, however, of remark in passing,
tained, were also those which he assigned to the that the modern world owes much to this error;
known world. His own account of its extent and for it tended to encourage that belief in the pracdivisions is given in the fifth chapter of his seventh ticability of a western passage to the Indies, which
book. The boundaries which he there mentions occasioned the discovery of America by Columbus.
are, on the east, the unknown land adjacent to There has been much speculation and discussion
the eastern nations of Asia, namely, the Sinae and as to the cause of Ptolemy's great error in this
the people of Serica; on the south, the unknown matter; but, after making due allowance for the
land which encloses the Indian Sea, and that adja- uncertainties attending the computations of discent to the district of Aethiopia called Agisymba, tance on which he proceeded, it seems to us that
on the south of Libya; on the west, the unknown the chief cause of the error is to be found in the
land which surrounds the Aethiopic gulf of Libya, fact already stated, that he took the length of a
and the Western Ocean; and on the north, the degree exactly one sixth too small, namely, 500
continuation of the ocean, which surrounds the stadia instead of 600. As we have already stated,
British islands and the northern parts of Europe, on his own authority, he was extremely careful to
and the unknown land adjacent to the northern make use of every trustworthy observation of latiregions of Asia, namely Sarmatia, Scythia, and tude and longitude which he could find; but he himSerica. self complains of the paucity of such observations;
He also defines the boundaries by meridians and and it is manifest that those of longitude must have
parallels, as follows. The southern limit is the pa- been fewer and less accurate than those of latitude,
rallel of 16 ~o S. lat., which passes through a point both for other reasons, and chiefly on account of
as far south of the equator, as MeroP is north of it, the greater difficulty of taking them. He had,
and which he elsewhere describes as the parallel therefore, to depend for his longitudes chiefly on
through Prasum, a promontory of Aethiopia: and the process of turning into degrees the distances
the northern limit is the parallel of 630 N. lat., computed in stadia; and hence, supposing the diswhich passes through the island of Thule: so that tances to be tolerably correct, his error as to the
the whole extent from north to south is 793~so, or longitudes followed inevitably from the error in
in round numbers, 800; that is, as nearly as pos- his scale. Taking Ptolemy's own computation in
sible, 40,000 stadia. Theeasternlimit is the meridian stadia, and turning it into degrees of 600 stadia
which passes through the metropolis of the Sinae, each, we get the following results. The length of
which is 119~0 east of Alexandria, or just about the known world, measured along the equator, is
eight hours: and the western limit is the meridian 90,000 stadia; and hence its length in degrees is
drawn through theInsulae Fortunatae (the Canaries) 906oo = 150o; the error being thus reduced from
which is 60?0, or four hours, west of Alexandria, 500 or 400 to 200 or 100. But a still fairer meand therefore 1800, or twelve hours, west of the thod is to take the measurement along the parallel
easternmost meridian. The various lengths of the of Rhodes, namely 72,000 stadia. Now the true
earth, in itinerary measure, he reckons at 90,000 length of a degree of latitude in that parallel is
stadia along the equator (500 stadia to a degree), about 47' = of a degree of a great circle = 47 x
40,000 stadia along the northernmost parallel 600 stadia = 470 stadia, instead of 400; and the
(2222 stadia to a degree), and 72,000 stadia along 72,000 stadia give a little over 153 degrees, a
the parallel through Rhodes (400 stadia to a de- result lamnost identical with the former. The
gree), along which parallel most of the measure- remaining error of 200 at the most, or 100 at the
ments had been reckoned. least, is, we think, sufficiently accounted for by
In comparing these computations with the actual the errors in the itinerary measures, which exdistances, it is not necessary to determine the true perience shows to be almost always on the side of
position of such doubtful localities as Thule and the making distances too great, and which, in this
metropolis of the Sinae; for there are many other case, wvould of course go on increasing, the further
indications in Ptolemy's work, from which we can the process was continued eastward. Of this
ascertain nearly enough whatlimits he intends. We source of error Ptolemy was himself aware; and
cannot be far wrong in placing his northern bound- accordingly he tells us that, among the various
ary at about the parallel of the Zetland Isles, and his computations of a distance, he always chose the
eastern boundary at about the eastern coast of Co- least; but, for the reason just stated, that least
chin China, in fact just at the meridian of 1 100 E. one was probably still too great.
Iong. (fromGreenwich),orperhapsattheoppositeside The method pursued by Ptolemy in laying down
of the Chinese Sea, namely, at the Philippine Islands the actual positions of places has already been inat the meridian of 1200~. It will then be seen that cidentally mentioned in the foregoing discussion.
he is not far wrong in his dimensions from north to He fixed as many positions as possible by their
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