Socrates. Very clever, by the Graces ! " '

At a much later period Pliny mentions that glass balls with
water put into them, when set opposite to the sun, get so hot
as to set clothes on fire ; and that he finds surgeons consider the
best means of cautery to be a crystal ball placed opposite to the
sun's rays. 2 The Chinese commonly use the burning-lens to
light fire with, as well as the flint and steel, and we hear of the
Siamese using it to produce new sacred fire. 3

The fact that fire may be produced by reflecting the sun's
rays with mirrors was known as early as Pliny's time (a.d.
23-79), as he remarks, " seeing that concave mirrors placed
opposite to the sun's rays ignite things more easily than any
other fire." 4 There is some reason to suppose that the know-
ledge of this phenomenon worked backwards into history, at-
taching itself to two famous names of old times, Archimedes
and- Numa Pompilius. The story of Archimedes setting the
fleet on fire at Syracuse with burning mirrors, probably un-
known as it was to historians for centuries after his time, need
not be further remarked on here ; but the story of Numa re-
appears on the other side of the world, under circumstances
which make its discussion a matter of importance to ethno-
graphy.
1 Aristoph., Nubes, 757, etc. 2 Pliny, xxxvi. 67, xxxvii. 10.
3 Davis, vol. iii. p. 51. Bastian, ' Oestl. Asien,' vol. iii. p. 516.
4 Pliny, ii. 111.
250 FIRE, COOKING, AND VESSELS.
