INDEX. 
Agate subject to almost endless variety — where found, voL iii. 
p, 414. Enhydres, what 415, Arborescent agates described, 
416. Mocha stones, what — -animal and vegetable substances 
converted into agate, 417- Mills employed to polish agates 
in Germany, 418. Chalcedony , from whence it derives its 
name — account of, 419 . Cornelian, where found — Sardo- 
nyx hardly separated from the carnelian — highly valued by the 
antients, 421. Onyx the hardest of the flinty tribe — used for 
cameos, 422. Artists celebrated for this mode of engraving, 
422, 423. 
Alabaster. See Stalactites. 
Aloe (American) its glorious appearance — opinion that it blows 
but once in a century unfounded, iii. 102. leaves described — 
aloe described by the Abbe La Pluche, 103. Medicinal 
aloe, account of — cultivation and mode of collecting the juice, 
105 — 108. Mahometans respect the aloe — -leaves of great 
use to the natives of Senegal, 109 . and to the poor in Mexico, 
110 . 
Amber varies in colour and degrees of transparency, iii. 476. is 
electric — where found, 477- particular specimens noticed — 
origin of amber involved in obscurity, 478. antient mytholo- 
gists account for its formation without any difficulty, 479. 
Ants fond of society — their city described— their persevering in- 
dustry exemplified, ii. 441. are good anatomists, 443. Dr. 
Franklin’s experiments to prove that ants communicate their 
thoughts to each other, 444. remain during winter ia a. lethar- 
