38 PHENOMENA obferved in the AIR VAULT 



from the knowledge I had acquired from my father Dr Roe-> 

 buck, and from my communications with other experienced 

 iron matters, that a great part of the power of fuch machinery 

 was mifapplied in general practice, by throwing air into fur- 

 naces with much greater velocity than necefTary, and that, if 

 this velocity was, to a certain degree diminifhed, the fame 

 power, by properly adjufting the blowing machinery, of what- 

 ever nature, would be capable of throwing into the furnace a 

 proportionally greater quantity of air. For, " Since the quan- 

 tities of any fluid, ijfuing through the fame aperture, are as the 

 fquare roots of the preffure j" it follows, that it would require 

 four times the preffure, or power, to expel double the quantity of 

 air, through the fame aperture, in the fame time : But if the 

 area of the aperture was doubled, then the quantity of air ex- 

 pelled by the fame power, and in the fame time, would be in- 

 creafed in the ratio of the fquare root of 2 to 1, though its ve- 

 locity would be diminifhed exactly in the fame proportion. 

 Again : I confidered that the quantity and intenfity of heat, 

 produced in blaft furnaces, and confequently its effects in in- 

 creafing the produce, might be only in proportion to the quan- 

 tity of air decompofed in the procefs of combuftion, without 

 regard to its greater velocity ; that is to fay, whether or not 

 the fame quantity of air was forced, in the fame time, into 

 the furnace through a fmall pipe, or through one of larger 

 dimenfions ; for, in attending to the procefs of a common air 

 furnace for remelting of iron, where there is a very large quan- 

 tity of air admitted through the large areas between the bars, 

 it is well known, that a much greater intenfity of heat is pro- 

 duced than takes place in a blaft furnace, and yet the air does 

 not enter into the fire through the bars with increafed den- 

 fity or great velocity. I therefore thought it probable, that in- 

 creafing the quantity of air, thrown into the blaft furnace in a 

 considerable degree, although the velocity or denfity might be 



much 



