20& IMPROVED LOCK TOR HOUSE DOORS. 



in the figure, and by condenfing the fleam, fufFers L again to 

 defcend ; and, after a vibration or two, the effect of the fleam 

 to raife the pifton and of the inje&ion to deprefs it, balance 

 each other, i'o that the levers remain nearly motionlefs. It is 

 evident that the injeclion will be lefs, the fleam flronger, and 

 the water which pafTes off through G hotter the nearer the 

 weight M is to the centre of motion. And in this refpect the 

 apparatus is fo effectual that the water may be heated to 210 

 degrees, and the quantity that pafles off is from 100 to 180 

 barrels per hour, according to the temperature, as governed 

 by the pofition of the weight M. 



XII. 



Dejrription of an improved Drawback Lock for Houfe Doors. By 

 Mr. Wm. Bullock. From the Tranfaclions of t/te Society 

 of Art*, zcho adjudged a Reward of Fifteen Guineas to the; 

 Inventor. 



Copy of a Letter to the Secretary of the Society Mr. Charles 

 Taylor. 



SIR, 



Inconveniences } HAVE herewith fent, for the infpecVion of the Society, an 

 the common improved Drawback Lock for Houfe Doors, &c. which im- 

 drawback. lock, provement is in latching the door ; for it is well known, par- 

 ticularly in damp weather, that the air drawing through it, 

 rufls the head or bevel of the bolt, by which means it requires 

 great force to fhut the door, and occafions a difagreeable noifc, 

 betides fliaking the building. 



It has frequently happened that the houfe has been expofed 

 to robbery from the door being left unlatched, when fuppofed 

 to be fail. This improvement removes all thofe inconveni- 

 ences, as it lets the bolt flioot into the ftaple immediately 

 when the door clofes, but not before ; and the reliever works 

 fo very cafy, that the door is made fall with one twenty- 

 fourth part of the force requirecLwith locks upon the common 

 conflruclion. 



By 



