DESCRIPTION OF A SECRET LOCK. 221 



And fo likewife in order to flop the bolt always at the fame Conrttu&ion of 

 point when fhut, there is fixed at Q, near the fhort edge bar, a a ^j* hck ac " 

 fcrew, the head of which (lands higher than the face of the bolt, t h e proprietor, 

 and flops it by taking again ft the box. When the bolt is re- 

 quired to be taken out, this fcrew is drawn back a little, and it 

 pafles clear of the edge bar. The fame effect might be ob- 

 tained by putting an interior ftem to the handle, which fliali 

 flop the bolt when the door is locked, which takes place when 

 the points X and X" coincide with' the faces of the pillars to- 

 wards the knob Q. This knob is alfo of ufe to open or bolt 

 the door within. The pofition of the knob Q is fuch, that the 

 circumference of its fcrew Item is a tangent to the line X X. 



The key remains to be defcribed : This is a circular plate or 

 difc, Fig. 6, of 50 in diameter and 3 in thicknefs. Its cir- 

 cumference is divided into 24 parts, carrying circularly the 24 

 letters of the alphabet, leaving out K. It has a handle in the 

 form of afemiellipfis, to turn it with the finger and thumb, and 

 this handle carries on the other fide of the plate two fmali fteel 

 points TT, of about 3 in length, which enter into the holes of 

 the fcrew heads. Laftly, This plate has an opening in its 

 center about 20 in diameter, to allow the points to be vifible 

 when applied to the fcrew heads. 



There are alfo marked on the face of the lock five fmali flars 

 or lozenges, to ferve as flation-points for the key ; and alfo five 

 fmali holes near one of the two holes of the fcrew heads. Thefe 

 fmali holes ferve as an indication to apply the key always in 

 the fame manner, by putting the fame point in the fame hole. 



The pofition of the four flars correfponding with the fer- 

 rils, muft be determined with great care and precifion. For 

 this purpofe, the ferrils muft be placed fo that their openings, 

 fhall be in a right line, and the holes of the fcrew heads in a 

 vertical line. The bolt is then to be introduced by engaging it 

 in the grooves of the pillars, fo that the four teeth or pins may 

 be lodged in the thicknefs of the ferrils. The turn-fcrew is 

 then to be inferted fucceffively in the holes of each fcrew-head; 

 obferving that the letter A, having its mark diftinguifhed by a 

 diamond, fhall be turned towards the Tame fide as the fmali in- 

 dicative point placed on the fcrew-head, and then a point muft 

 be made on the face of the lock to correfpond with the letter 

 A of the key. At this point the flar is to be made, which will 



be 



