36 PHENOMENA obferved in the AIR VAULT 



and converted into vapour, -was able to force its way through the 

 pores of the rock into the vault, but that being in a manner con- 

 fined within the rock, by the preflure of the condenfed air, 

 it found itfelf at liberty to come into the vault, only when 

 the condenfation abated confiderably, or was totally removed 

 by the going flow, or flopping of the engine. It alfo occurred 

 to me, that the air, in a flate of condenfation, might poffibly 

 be capable of holding a greater quantity of water in folution, 

 which might precipitate fuddenly into vapour or mifl when 

 the condenfation abated. I imagined, therefore, that the very 

 fmall quantities of water we at times difcovered, proceeded 

 from nothing elfe but this vapour, in its paffage to the furnace 

 along with the blafl, being condenfed into water, by the cool- 

 nefs of the eduction pipe and iron wind cheft. The quantity 

 of water did not appear to amount to a gallon in twenty-four 

 hours. 



A few days after I had made this experiment, the water cea- 

 fed entirely to make its appearance, either at the tweer, or at 

 the hole in the wind cheft ; but the furnace did not come into 

 heat for a long while after, and indeed not till the keepers let 

 much more air into it by a larger blow-pipe, and allowed lefs 

 air to efcape at the fafety valve. It is probable that the rock 

 was now become perfectly dry by the continued heat of the fur- 

 nace. 



My experiment had the good effect to remove all the pre- 

 judices againft the plan I had adopted of blowing the furnaces, 

 and likewife prevented the other partner from laying out a large 

 fum of money, by flopping the works, and altering the blowing 

 machinery. Indeed, it has fince been admitted, by all who have 

 feen it at work, to be the moll fimple and effective method of 

 equalizing the blafl of any yet put in practice. 



This experiment led me, fome time afterwards, to apply a 

 wind guage that I contrived, to afcertain precifely the flate of 



the 



