Note 20 — BOOK VI. (continued 2)

[Pg 210][20] Pliny (XXXI, 28). "In deep wells, the occurrence of sulphurata or aluminosa vapor is fatal to the diggers. The presence of this peril is shown if a lighted lamp let down into the well is extinguished. If so, other wells are sunk to the right and left, which carry off these noxious gases. Apart from these evils, the air itself becomes noxious with depth, which can be remedied by constantly shaking linen cloths, thus setting the air in motion."