tf the Devon Iron-Worh. 529 



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 perfeftly dry by the continued heat of 

 the furnace. 



My ex'perimcnt had the good effect to remove all the pre- 

 judices againft the plan I had adopted of blowing the fur- 

 naces, and like wife prevented the other partner from laying 

 "out a large funi of money, by flopping the works, and alter- 

 ing the blowing machinery. Indeed, it has fince been ad- 

 mitted, by all who have feen it at work, to be the moft 

 fimple and effedlive method of equalifing the blaft of any yet 

 put in practice. 



This experiment led me, fome time afterwards, to apply 

 a wind-gauge that I contrived, to afcertain precifely the Hate 

 of the condenfation of the air thrown into the furnaces. I 

 found that a column of quickfilver was raifed five inches; and 

 fometimes, though feldom, fix inches; and, in the interval of 

 the return of the engine to receive air into the air-pump, it 

 fell only half of an inch. At this time only one furnace was 

 worked. But when two furnaces were in blaft, the engine 

 only raifed the mercurial gauge about four inches ; becaufe 

 the Devon company, for certain reafons, did not, while I 

 continued a partner, think proper to allow the blovi-ing ma- 

 chinery to be completed, by the putting to work their fecond 

 boiler of twenty feet diameter for the fire-engine, according 

 to my original defign, which, by adjufting the machinerv, 

 would have enabled us to blow two furnaces, with two boil- 

 ers, with as much effect, in proportion, as one furnace with 

 one boiler. This inftrument had the advantage of enabling 

 the work-people to difcover the real power of their blaft, and 

 know the exaft condition of the air-valves, and the gearing 

 of the blowing: pifton; for, if thefe were not tight, and in 

 order, (although tlie engine might, to appearance, be doing 

 well, by making the lame number of difcharges of the air- 

 pump as ufua! per minute,) yet the wind-gauge would not 

 rife fo high, and would (liow that there was an imperfection 

 fomewhere, by reafon of a quantity of air efcaping at the' 

 valves, or pifton, that could not foteafilyotherwife beknowa. 

 -Vox. VI. U u Thi» 



