204 DESCRIPTION OF AN ANCIENT LOCK. 



box opened, unlefs one particular point of the fun, and each 

 of the hands be duly placed from a knowledge of the fecret. 

 And as there are twelve points to' the fun, and twelve marks 

 for the hours on each dial, we may (without confidering the 

 probability of intermediate pofitions) reckons the chances 

 as eleven to one, againft fetting the fun to the proper pofilion; 

 and eleven times ftill more againft fetting the fun and face of 

 The fecret of t ^e dials right at the fame time ; and again eleven times more 



the lock is fe- . * ° , ■ ° 



cureasi33itoi. againft all thefe being duly fet at once. That is to fay, the 

 chances are 11 times 11 = 121, taken 11 times or = 1331. 

 And confequently the lock is very fecure. 



As I hope foon to give a fhort eflay on locks, I (hall only 

 make a few remarks on the prefent machine. In the firft 



Cardan's lock. p]ac ^ it may be not iced that this> like the j ock of Cardan *, 



which confifts of four or more rollers, is a fecret lock, and 

 not a lock of combination ; this laft term being ufually applied 

 Sacret locks and to locks in which a fecret can be changed through a great 

 binatkxn. number of varieties, at the pleafure of the owner. And, 



fecondly, that it has a practical defect very common to all 

 fecret locks; namely, that a ikilful examiner may difcover 

 the fecret, if the workmanthip be in the fmalleft degree in- 

 Thc prefent accurate. In this manner I opened the prefent lock, at the 

 opened. * ver y nr ^ trial. ^ tne tnree notched pieces be not truly 



circular, and the motion of the bolt extremely precife, and 

 the lengths of the tails accurately adjufted, one of thefe tails 

 will bear before the other. I therefore prefled the bolt back, 

 by urging the figure of the moon towards that of the fun, and 

 then turned the three pieces round one after the other. Two 

 of them moved freely round, and the third gave notice when 

 the bolt fell in, and confequently told its fecret. Of the re- 

 maining two pieces, one moved freely, and the other hung 

 and (hewed its pofition. And laftly, the third then required 

 only to be moved till the bolt took its notch, and went quite 

 back. 

 Bot It may be This lock could be eafily made fafe, by adding mort teeth 

 roadefafebya t the infide pieces all round, and making the tails of the 

 2aagel. S DoIt terminate in fmall projections adapted to take between 



thofe teeth. By this contrivance, the tentative procefs of 

 turning the pieces would be rendered impracticable. 



* The fecret padlock of four rollers is fold at our ironmongers. 

 I bought one at Downer's in Fleet Street, for fixteen pence. 



It 



