5220 DESCRIPTION OF A SECRET LOCK. 



Conftruftion of The diftances of all thefe points from the extremity C C of the 



a fee ret lock ac- 1 i, ■ ,., , , ,, <„ 



ceffibleonlyto boIt are » namely, httle c x 20, ex 60, c x 226, ex" 274, 

 Ihe proprietor. C F 310. 



In order to complete the bolt, it only remains to fix its rack 

 and its four pins correfponding with the four ferrils. 



The rack is a rectangle, of which the length is M N, Fig. 5, 

 equal to 67, the breadth or depth M M' 33, and the thicknefs, 

 which could not be fhewn in this figure, is 4, and maybe feen 

 in Fig. 3. This parallelopepidon is fixed perpendicularly upon 

 the bolt at M' N', Fig. 3, by two projecting rivets K K> 

 Fig. 5. 



The rack is notched fo as to form in its length M' N 7 , 13 

 teeth of 5 in depth ; fo that it refembles a comb with very 

 fhort teeth. The fpaces are wider than the teeth, and they 

 are rounded on the fide which locks into the wheel. 



The fingle tooth or pin which is intended to correfpond to 

 each of the ferrils, is formed of four parts, ftand up at right 

 angles, as is feen in Fig. 4. O H is the pin. properly fo called, 

 rivetted perpendicularly in the bolt by the fmall fquare extre- 

 mity H. I I are two fmall wedges which precede the tooth. 

 OH is J 1, and I I 16. 



The diftance of the tooth or ftud O from the line C C, Fig. 

 3, is 39; that of O' is 1 18 ; that of O" is 169; that of 

 0"'24S. 



The little wedge which precedes the tooth, is 6 in length 

 and 3 in height. We (hall hereafter fee the ufe of this. 



From the pofition of thefe four ftuds it follows, that when 

 they are lodged precifely in the thicknefs of the ferrils, the two 

 extreme ferrils muft have their long notch or aperture directly 

 towards the extremities of the lock, and thofe of the interme- 

 diate ferrils will, on the contrary, have their apertures both 

 turned towards the middle wheel. We fhall fee alfo that it 

 follows, that when the lock is open, the firft pin O is out of the 

 lock in the groove cut in the door ; the tooth O' is within the 

 fecond ferrol; the tooth O" in the fpace above the wheel ; and 

 the tooth O"' within the fourth ferril. And the contrary is 

 the cafe when the door is fhut. 



In order that the bolt may flop at the fame point when the 

 door is open, there is a fmall protuberance X or X"'. The 

 teeth O, O', O", O'", are then fufficienlly difiind from the fer- 

 rils to allow of their being moved or fet. 



And 



