IZ? Of THE VENTS,

ductile metal, as pure copper; so that when P L is stronglyscrewed down, the plate may spread and fill up the spacebetween P and H F so exactly, that none of the elasticfluid may be able to penetrate among the spirals. The for-mula (126) will serve to compare the resistance with theforce of the powder, that acts against the base K N of thebouch; 4981 nrc expresses the force of the powder, cmq

KN

the resistance of the bouch ; put ——- in the place of r and

the circumference corresponding to the diameter K N in theplace of c. If the circumference = c correspond to the dia-meter B D of the spirals, then in the second formula put thelength L P in the room of m\ and since circumferences areproportional to their diameter s, th ese may be substituted andthe formulas will be 2460 flxKN 1 , BDxLPxQ.

try- The resistance of bouches made on this principlehave been found more than sufficient in practice. Theexperiments made in 1771 prove the goodness of the bouches;(Fig. 9 and 13) their resistance is amply sufficient, andwhen damaged they may be easily taken out and replaced(127). The bouch (120) was neither moved or corrodedin the 800 rounds fired from the Sarcophagus', and the famewas the result of the experiment (34) with a bouch (Fig. 13).When the bouches were taken out, neither the male norfemale screws were in the least altered, nor had the elasticfluid or the water which remained in the gun for 5 hourspassed the ledge B D. In the gun called the Paphos, whichin 1771 was fired in the fame manner as the Invincib’e (34Jwith a bouch (Fig. 13), the fame effects were observed.The operation of taking out and rep’acing the bouches takespp but a few minutes ; it may be performed upon the batte-ries without dismounting the guns.

C l! A ?.