DESCRIPTION OF A SECRET LOCK. 279 



1th, The lock is veryfolid; for there is no opening into Conftruclion of 

 which any tool might be introduced. The face of the door a fecrct lock ac- 

 may likewife be furrounded with a ftrong metallic covering let ^ p ropr i c tor, 

 into the wood, and the back part of the door may be covered 

 with iron plates, the only method of preventing any one from 

 cutting the wood round the lock. 



Sth, If it mould be thought inconvenient to place the lock in 

 the thicknefs of the door it may be eafily avoided. The items 

 of the fcrew-heads need only be made longer, and another 

 plate fimilar to that of the face, added : the fcrews in that 

 cafe, after having pafled through the face as well as the door, 

 would pafs into the lock. This addition requires an increafe 

 of work, but it affords no real advantage. 



Lock for a Bureau or Secretary, 



Though my lock, as I have defcribed it, can be eafily fixed 

 to a fecretary, yet I think it ufeful to indicate the changes con- 

 venient to be made in it. 



lft, The height of the ferrils muff be diminifhed, that the 

 bolt may be intirely funk in the flap of the fecretary. 



2d, In order to diminifh the length and breadth of the lock, 

 ten divifions in the ferrils may be made inftead of eighty ; they 

 need then be only 25 in diameter; but then the fecret will 

 confift in a number of four figures inftead of a word of four let- 

 ters, which is not fo convenient, as I have already obferved. 



3d, The box of the lock may be fuppreffed, and the lock will 

 ftill have folidity furficient for a bureau ; the price will likewife 

 be diminifhed. 



Uh, Inftead of engraving characters on the face of the lock, 

 I prefer, as has been feen, to mark them on the turnfcrew itfelf ; 

 but the external damage is not to be feared in a fecretary as in 

 a door. It is therefore more convenient that the figures or 

 letters mould be on the faee itfelf of the fcrew, and a knob or 

 fmall handle may be contrived on the face of the fcrews, in 

 ©rder to turn them. In this cafe no key or turnfcrew need be 

 carried about; this is an advantage of fome confequence. 



Concerning fome other Kinds of Compound Locks. 



It is poflible, as I have already obferved, to apply the prin- 

 ciples of thefc combinations to the construction of locks in a* 



number 



