CI. But what above all makes writing history a difficult task is, that,
in order to be a historian, it is necessary for a man to be much more
than a historian. This, which may appear a paradox, is not so, but a most
true position: I mean, that a person can’t be a perfect historian, who
has not studied other faculties besides history; because, in various
instances, a knowledge of other faculties discovers the falsity of
some historical relations. The understanding geography, for example,
no one can deny to be exceedingly necessary. Polybius and Diodorus
Siculus, were so diligent in this matter, that before they wrote their
histories, they travelled over the kingdoms and countries to which they
related. Now-a-days this labour is not necessary, because the numbers
of geographical books and maps at present extant, although they are not
minutely exact, are sufficiently correct to make this trouble needless.
CII. Besides, there is another circumstance, which perhaps as yet,
has never been attended to, which is, that other faculties which are
seemingly very foreign from history, often serve to throw lights on
various occurrences. What faculty, for example, to appearance, can have
less relation to history than astronomy? but Quintus Curtius, through
his gross ignorance of this science, fell into an historical error. He
says, that when Alexander was marching to India, his soldiers complained
loudly, that he was leading them to a country where they should not be
able to see the sun. They might have had reason for this complaint, if
he had been marching them Northward, in consequence of which, they would
have perceived the sun to get lower, and the days to shorten upon them;
but by marching towards the South, as they then were marching, they
must observe the sun to get higher, and consequently, that fear in the
soldiers could not have been possible.
CIII. Who would think of supposing, that optics and catoptrics, and
we may say the same of other mathematical subjects, could be of use
in writing a history? But please to observe, that by understanding
optics, you would know, what Valerius Maximus, and other authors, tell
us of a man named Strabo, who, from the promontory of Lilibyum, saw and
counted the ships that had just sailed out of the port of Carthage was
impossible, because the image of every ship, which at such a distance,
could be formed on the retina, must be so exceedingly minute as to have
been imperceptible. Also by understanding catoptrics, would be known
either the impossibility, or almost insurmountable difficulty of making
the burning glasses, with which we are told Archimedes, at the siege of
Syracuse, set fire to the ships of Marcellus; that is, if we suppose the
ships to have been as far distant from the walls as some authors have
placed them, which was more than thirty geometrical paces.
CIV. Finally, and to sum up the whole, as human events which are the
object of history, may bear analogy to the objects of all sorts of
faculties, there is not one of them, which by an historian’s being
acquainted with may not afford assistance in the discovery of the truth
of some facts.