SgCRET LOCK. 161 



fwve to move the four wheels feen in Fig. I. Thefe wheels Defcription of a 

 have twelve teeth each, and are fattened by center-fcrews, "o^j,°njt;on, 

 each upon a flat wheel of the f^me tooth ; but having only ten 

 notches aflually cut, as is feen in the right hand upper corner, 

 where one of the upper wheels is taken off, and is fhewn at 

 fig. 3. Thefe upper wheels have their toothed part confi- 

 derably higher than the interior or flat part ; fo that they 

 would be contrate wheels if the teeth were cut quite through. 

 But this is not the cafe, except with two of the notches, as 

 may be feen in the two lower wheels more particularly, and 

 alfo in the others. The upper wheels have alfo two of the 

 notches between the teeth flopped up, as is Qiewn in Fig. 3; 

 by which contrivance there are but ten fituations for fcrewing 

 each wheel upon its correfpondent under wheel ; and thefe 

 fituations are rendered precife, and all relative motion between 

 the two correfpondent wheels prevented by a fmall ftud feeri 

 in the uncovered wheel, Fig. 1, which fits into one of the 

 notches of the upper wheel when put in its place. The upper 

 wheel has a number on each tooth from I to 9 and 0, which 

 are of ufe for placing this ftud. The four under wheels are 

 held in their fituations by four fpring-catches, which allow 

 them to be turned, in one diredion only, by means of their 

 knobs or handles 9 and when any wheej is thus turned round, 

 the finger and thumb will feel the flroke of the lever, as it 

 fucceflively falls into each notch, until the lever comes to refl 

 upon the fmooth part. This very palpable indication then 

 fliews when to begin to count, calling the firfl hold or flroke 

 of the catch 1 ; the fecond 2 ; the third 3, &c.; and the lock 

 is fo conftruded, that when the top wheel of any of the four 

 couple is, put on with any number oppofite the flud, the 

 fame number counted by the catch will place the upper wheel 

 in fucb a fituation, as that its notches, which pafs clear 

 through, will lie in a circle defcribed from the center or axis 

 upon which the great handle turns. And therefore, when 

 each of thefe wheels is put in its place, and the numbers known 

 {and regiftered, or put in the memory by fome artificial afTo- 

 ciation, fuch as of the date of the year taken either backwards 

 or forwards, &c.) it is only needful to move each of the four 

 knobs till its catch has palTed the fmooth part, with a number 

 of flrokes anfwering to its adjuftment, and the circle indicated 

 by broken fhaded lines in Fig. 1, will be capable of paffing 



through 



