THE EARTH. 39 



*f. e pit where they were then employed. By great good fortune, thej 

 at that time perceived their error, and instantly fled for their lives 

 The next day, however, they were resolved to renew their work in the 

 same pit, and eight of them ventured down, without any great appre- 

 hensions ; but they had scarce got to the hottom of the stairs that le<? 

 to the pit, when, coming within the vapour, they all instantly dropped 

 down dead, as if they had been shot. Amongst these unfortunate poor 

 men, there was one whose wife was informed he was stifled in the 

 mine ; and, as he happened to be next the entrance, she so far ven- 

 tured down as to see where he lay. As she approached the place, 

 the sight of her husband inspired her with a desire to rescue him, 

 if possible, from that dreadful situation ; though a little reflection 

 might have shown her it was then too late. But nothing could deter 

 her ; she ventured forward, and had scarce touched him with her 

 hand, when the damp prevailed, and the misguided, but faithful crea- 

 ture, fell dead by his side. 



Thus the vapours found beneath the surface of the earth, are very 

 various in their effects upon the constitution : and they are not less in 

 their appearances. There are many kinds that seemingly are no way 

 prejudicial to health, but in which the workmen breathe freely; and 

 yet in these, if a lighted candle be introduced, they immediately take 

 fire, and the whole cavern at once becomes one furnace of flame. In 

 mines, therefore, subject to damps of this kind, they are obliged to 

 have recourse to a very peculiar contrivance to supply sufficient 

 light for their operations. This is by a great wheel ; the circumfer- 

 ence of which is beset with flints, which, striking against steels placed 

 for that purpose at the extremity, a stream of fire is produced, which 

 affords light enough, and yet which does not set fire to the mineral va- 

 pour. 



Of this kind are the vapours of the mines about Bristol: on the 

 contrary, in other mines, a single spark struck out from the collision 

 of flint and steel, would set the whole shaft in a flame. In such, 

 therefore, every precaution is used to avoid collision ; the workmen 

 making use only of wooden instruments in digging ; and being cau- 

 tious, before they enter the mine, to take out even the nails 

 from their shoes. Whence this strange difference should arise, that 

 the vapours of some mines catch fire with a spark, and others only 

 with a flame, is a question that we must be content to leave in ob- 

 scurity, till we know more of the nature both of mineral vapour 

 and of fire. This only we may observe, that gunpowder will readi- 

 ly fire with a spark, but not with the flame of a candle : on the 

 other hand, spirits of wine will flame with a candle, but not with 

 a spark; but even here the cause of this difference as yet remains 

 a secret. 



As from this account of mines, it appears that the internal parts 

 of the globe are filled with vapours of various kinds, it is not surpris- 

 ing that they should, at different times, reach the surface, and there 

 put on various appearances. In fact, much of the salubrity, and much 

 of the unwholesomeness of climates and soils, is to be ascribed to 

 these vapours, which make their way frorc the bowels of the earth 

 upwards, and refresh or taint the air with their exhalations. S.'iri 



