[197] [Sextus Empiricus (Adv. Math. cap. 21) says that the Chaldæans
divided the zodiac into 12 equal parts, as they supposed, by allowing
water to run out of a small orifice during the whole revolution of a
star, and dividing the fluid into 12 equal parts, the time answering
to each part being taken for that of the passage of a sign over the
horizon.]
[198] Lib. ix. c. 9.
[199] [Some mode of measuring time by the reflux of water, however rude
it might be, was used at Athens before the time of Ctesibius, as we see
by various passages in Demosthenes.]
[200] Auctor Dialog. de Caus. Cor. Eloq. 38.--The orators were confined
to a certain time; and hence Cicero says, _latrare ad clepsydram_.
[201] Some account of the writers who have spoken of the water-clocks
of the ancients may be found in Fabricii Bibliograph. Antiquaria,
p. 1011. They were formerly used for astronomical observations. The
authors who treat of them in this respect are mentioned in Riccioli
Almagest. Novo, i. p. 117.
[202] In that year Kircher’s Ars Umbræ et Lucis was published for the
first time. In the edition of 1671, several kinds of water-clocks are
described, p. 698.
[203] A particular account of these water-clocks is to be found in
Ozanam, Recréations Math. et Physiques [republished in Hutton’s
Mathematical Recreations, ii. 40]. Bion on Mathematical Instruments.
[204] Muschenbroek, Philos. Natur. i. p. 143.
[205] Journal des Sçavans, 1691.
[206] This monk may be considered as the restorer of the clepsydra,
or clock which measures time by the fall of a certain quantity of
water confined in a cylindric vessel. These clocks were in use
among ancient nations. They are said to have been invented at the
time when the Ptolemies reigned in Egypt. Dom Vailly, who applied
himself particularly to practical mathematics, having remarked the
faults of these clocks, bestowed much labour in order to bring them
to perfection; and by a number of experiments, combinations, and
calculations, he was at length able to carry them to that which they
have attained at present. At the time of their arrival they were very
much in vogue in France.--Hist. Littéraire de la Congr. de St. Maur,
ordre de S. Bénoit. Bruxelles, 1770, 4to, p. 478.
[207] Ozanam, ii. p. 475.
[208] Alexander will not admit this to be the case. “It is possible,”
says he, “that two persons of penetrating genius may have discovered
the same thing.”
[209] Art du potier d’étain, par Salmon. Paris, 1788, fol. p. 131.