Note 988 — Chapter I

We extract the following notice on this passage from Humboldt (Cosmos, vol. iii. 54, Bohn’s edition). “This passage has recently been pronounced corrupt, (Kramer i. 211,) and δι’ ὑάλων (through glass spheres) substituted for δι’ αὐλῶν (Schneider, Eclog. Phys. ii. 273). The magnifying power of hollow glass spheres, filled with water, (Seneca i. 6,) was, indeed, as familiar to the ancients as the action of burning glasses or crystals, (Aristoph. Nub. v. 765,) and that of Nero’s emerald (Plin. xxxvii. 5); but these spheres most assuredly could not have been employed as astronomical measuring instruments. (Compare Cosmos i. p. 619.) Solar altitudes taken through thin light clouds, or through volcanic vapours, exhibit no trace of the influence of refraction.”