of the Devon Iron^Worh. 333 



But an unfortunate dlfagreement among the partners of 

 the Devon company put it out of my power to make further 

 progrefs in this matter, by laying me under the neceffity, 

 two years ago, of withdrawing myfelf entirely from the 

 concern. 



In order to illuftrate what is faid above, a ground plan of 

 the air-vault and furnaces of the Devon iron-works is given 

 in Plate X. of which the explanation follows : 



Explanation of Fig. l. Plate X. 

 A the air-vault, formed by a mine drove in the folid rock 

 of coarfe grained freeftone. B the blowing cylinder. C the 

 pipe that conveys the air from the blowing cylinder to the 

 air-vault. D, the eduaion-pipe, that carries the air from the 

 air-vault to the iron wind-cheft. E, the iron wind-cheft, 

 (about 2. \ feet cube,) in which is inferted a wind-gauge, re- 

 prefented in Fig. 3. FF, the two blow-pipes for each fur- 

 nace, which terminate in apertures of 3^ inches diameter at 

 the tweers of the furnaces. GG, the two blaft-furnaces, 

 placed in two pits funk in the folid rock. HH, the timps 

 of the furnaces, from whence the caft iron is run oif into the 

 cafting room LL. O, the door to give occafional admittance 

 into the air-vault. M, the excavation, in which is placed the 

 blowing machine. 



Explanation of Fig. 2. 

 A, the end of the wind-gauge, (about I3 inches long,) 

 which is open to the atmofphere, being half fdled withquick- 

 filver. B, the end that is inferted in the iron wind-cheft, and 

 expofed to the preffure of the condenfed air of the air-vault. 



Alfo. bccaufe V =: §r, and alfo V= :^, 0= Dv'P, fo that, while 



P remains the fame, Q^vvill increafe as D increafes, and V will diminifh 

 in the fame ratio. 



The problem, therefore, of throwing the greateft quantity of air into 

 the furnace, with a given pDwer, ftrlftly fpeaidng, has no maximum, but 

 the largtft aperture of which the engine can admit mull be the left. It 

 ii probable, however, that there is a certain velocity with which the air 

 ought to enter into the furnace ; this will produce a limitation of the pro- 

 - plcm, which, as Mr. Roebuck fuggefts, is not likely to be difcovered but 

 t,y experiment. J- P. ^^^ ^^^^_ 



