DESCRIPTION OF A SECRET LOCK. 2SJ 



the 24 fmall fcrew-heads might be fubftituted for the flops, Conftruftionof 

 which would not then require ferrils. This arrangement would ceffibk only to" 

 not be preferable to the other. the proprietor' 



2d, Let us imagine three rings lodged one within the other, 

 and forming one and the fame plane with a fourth fixed to the 

 door, and an immoveable circle in the centre ; fuch is the face 

 of the lock. The three intermediate rings turn freely and fe- 

 parately by means of a button, which muft be made to corre^ 

 f'pond with one of the letters of the alphabet marked on the 

 outer circle fixed to the door. Each carries interiorly a ferrii 

 capable of 24 pofitions. When the notches of the three ferrils 

 are difpofed in ftraight lines, the bolt is made to move by mean* 

 of a knob or handle in the middle of the face. 



This lock* refembles in feme refpeds the firft I have de- 

 fcribed. In this the ferrils are concentric, and in the others 

 they are feparate. It has an agreeable form, and would be 

 proper for a fecretary, and its execution does not require much 

 precifion. It is not very convenient for a door, becaufe it is 

 likely to be damaged. 



3d, Let us imagine five fcrew-heads on the face j let each 

 of thefe fcrews carry a fmall pinion within, which moves a 

 notched bar or rack. This rack muft have ten teeth, one of 

 which is withdrawn, in order to leave a clear way or fpace. 

 The fifth fcrew muft move a fifth rule carrying four teeth, and 

 at right angles to the other four. It is clear that this laft rule, 

 which I fuppofe to be the bolt, can never move except when, 

 the other four rules are in a convenient pofition. In this me- • 

 thod the lock will be enormoufly large ; and it will alfo be very 

 difficult to prevent this fecret from being difcovered from 

 without. 



4-th, If toothed wheels, with an unequal number of teeth 

 all taking in one another, be fubftituted for the fiat wheels 

 which are under the ferrils in the fyftem of locks with fcrew- 

 heads, then, if one fcrew-head be moved, it will derange all 

 the ferrils at once. This faves time, without diminifhing the 

 number of combinations. This advantage led me to approve 

 of the conftruclion for fome time ; but it is productive of fo 

 many ferious inconveniences, that I was obliged to aban- 

 don it. 



* I have feen fome* at Paris, nearly flrmlar to this. 



It 



