276 DESCRIPTION OF A SECRET tOCK 



IX. 



Defcription of a nezv Secret Lock. % J. B. Berard. 



(Concluded from Page 222 J 



Conftmaion of I MAY alio in this place ftate the reafon why I have made 

 a fecret lock ac- the k as we jj as the ferr j| s ^h ^ ^^ ^^ 25 Jivifions. 



ceflible only to /-^ , 



the proprietor. In the hrlt place, it affords a (mall diminution in the dimenfions 



of the lock. Another more effential advantage is, that in the 



divifion of 24, each notch in the ferril is oppofed to another 



diametrically oppofite, which facilitates the introduction and 



taking out of the bolt. We may obferve, that for the fame 



reafon the teeth of the ferrils, being rather rounded at the 



tip, facilitate the entry of the little wedge, which is likewife 



rounded underneath. 



The lock being thus conftru&ed, it only remains to fix it to 

 the door. For this purpofe, an opening is contrived of the iize 

 of the box of the lock, in the horizontal crofs piece, without 

 cutting the vertical frame of the door; and round it a groove 

 is made, of 2 in depth and 6 in breadth, on which the face of 

 the lock refts : the lock is placed in this opening without the 

 bolt; and if it is defired, four nails or fcrews may be driven 

 into the wood through four holes made in the face of the plate- 

 but this is not neceffary. The bolt is then placed on the other 

 fide of the door, and if the wood be too thick, it may be cut 

 away till the bolt Aides fair and eafily over the wood. This 

 is very eafy to be done, and then the face of the bolt ought to 

 lie flulh with the edge of the door. 



It is obvious that the height of the ferrils mutt be propor- 

 tioned to the thicknefs of the door. If the door be 30 m. 

 thick, for example, the ferrils (which ought to be 1 under the 

 furface of the lock) would be about 29. 



I muft alio obferve, that in order to render the motion of the 

 fcrew-heads more eafy and uniform, a pafteboard of 1 in thick- 

 nefs, with five holes punched in it, muft be laid upon the inner 

 furface of the plate of the lock ; and above the pafteboard, 

 another ilip of very thirf brafs, likewife perforated with five 

 holes : then the interior flat wheels have a very eafy motion 

 3 over 



