(J34 PHILOSOPHICAL TRANSACTIONS. [anNO J 762. 



while the water flows from the cistern d through the tube qcp into the vessel b. 

 At the orifice of this, snow and ice are generated, p and s are small valves, to 

 prevent the return of the air from the vessel b, and the water from the tube fs. 



The operation of the machine is performed thus : two men being ready at the 

 vessels, and the cocks being all shut, and sufficient water being let into the tubes 

 RT and GT, from the cistern n or o ; first they open the cocks c and e of the 

 lower vessel, and quite fill the lower vessel with water from the cistern d. Then 

 the cocks c and e are shut, and h and l of the upper vessel opened, so that the 

 water, flowing in through hx, may leisurely fill the vessel, and compressing the 

 air, thus force it through lmm into the lower vessel; the water begins then to 

 flow out at F, till the vessel a be hardly half full. The vessel b being thus 

 nearly emptied, h is shut, and the pipes k and i opened, the greater part of the 

 water is let out of the vessel a. Then k and i are shut again, l opened, and the 

 air returns into the vessel a with a loud noise. Lastly l being closed, the opera- 

 tion is finished, till it be proper to repeat it. 



When the work is performed with the water from the cistern n, which is satu- 

 rated with nitrous and sulphureous particles, if in the foregoing operation, the air 

 being returned by opening the cock l, and the tubes c and e opened, a kind of 

 snow is always generated at the orifice of the tube e, and collected like a cap 

 about it. But if, after the said operation, the cock l be not opened, and so the 

 air remain in a state of compression, on opening the tubes c and e, the cap, in- 

 stead of snow, is formed into a firm and thick cap of ice. But nothing of this 

 kind happens when the operation is performed with the rain water from the 

 cistern g. 



The measures of the parts are as follow ; — 



Of the vessel a, the diameter 494^ inches, height 54 inches, thickness l^- inch. 



Of the vessel b, the diameter 324- inches, height 60 inches, thickness 1± inch. 



The tubes rt, gt of iron, diameter 4-j. inches, thickness I4- inch. 



Also the diameter of Fsa 3i inches, lmm tapering, has the upper diameter 2 

 inches, the lower 1 inch, and thickness 1^ inch. 



The Chemnic foot is to the Paris, as 1538 to 1440, the pound as 106 to 92. 

 A cubic foot of the mine water weighs 72lb. 



The vessel a contains 57-^ cubic feet, b 274- cubic feet, or 22 amphoras. 



At each operation there is raised 25 cubic feet, sometimes 31 4, difi^ering only 

 in time, as the water flows in fi-om n or from o ; and there will be performed 

 20 or 21 repetitions of the operation in the one case, in the other only 17 

 or 18, 



