Mine ventilation in New Spain: foul air, a furnace draught and a royal article

A law book printed at Madrid in 1761 for the mines of New Spain turns from drainage to a second killer: the corrupt vapours the operarios must flee to avoid suffocating. It prints, with two figures, a furnace ventilator drawing the underground air out by a chimney, recommended because it spares the workmen the labour of bellows — and claims none of the invention as its own. In 1783 the crown made free ventilation a condition of every drainage adit.