68 Detail of the ConftruSlion of 



cafe neceffary to retouch the notch itfelf. The requifite degree of precifion may be eafily 

 obtained, when, upon examining with attention the print of the characters engraved upon 

 the p]ate, the inequalities fliall have been afcertained by a very fine line pafling exaftly under 

 the bafe of two fimilar letters, aflumed as objefts of comparifon : for the irregularity of linear 

 pofition may, by tliis means, be determined, with great exadnefs, and remedied to the moll 

 extreme nicety. In this operation, the workman muft file away part of that furface of the 

 notch which is oppofite to the direction of the motion the character requires. Great care 

 muft be taken to file only a fmall portion at a time, in order that the inftant may be 

 feized at which the wedge, by entering into the notch, brings the charadter to its due 

 fituation. 



Thefe details refpe£ling the right-lined arrangement on the charadters, muft not divert our 

 attention from the very great celerity with which any letter is brought to its place under the 

 prefs, by means of the regifter and detent. This celerity is an objedl of fo much importance 

 in the engraving of a great work, that every means ought to be purfued which may tend to 

 increafe it. For this reafon it is, that inftcad of following the alphabetic order in the arrang- 

 ment of punches on the furface of the wheel, we ought to prefer that in which the fum 

 of the different motions to be given to the wheel, for engraving an entire work, fhall be the 

 leaft poflible. This tedious enquiry may well be difpenfed with, by obfervifig the order in 

 which printers diipofe their cafes of characters, that the letters of the moft frequent recurrence: 

 may be moft immediately under the hand of the workman. 



■ If all the charaiSers afforded an equal refiftance to impreflion in a plate of metal, a coirftant 

 force would never fail to drive the punches to the fame depth. But the faces of the letters 

 Sre very unequal, and, confequently, it will be neceffary to ufe a variable force. Moft work- 

 men ufe the hammer, and not a fcrew, as in this machine, for ftamping. If the hammer had 

 been ufed in this machine, it is evident that if we fuppofed it to have fallen from the fame 

 height upon every one of the punches, the force of the ftroke could be rendered variable ac- 

 cording to the nature of the characters, by placing a capital, or head, upon each, of an height 

 properly adjufted to receive the hammer after pafling through a greater or lefs fpace. But 

 the heads of our punches are variable at pleafure, becaufe they are fcrewed on ; and thus it i& 

 that, by experimentally adjufting the heads of all the punches, a fet of impreflions are obtained, 

 of equal depths from every one of them. When, for example, the letter / is placed under the 

 hammer, the upper part of its head is at a fmall diftance from the head of the hammer, in 

 order that its fall, which begins always at the fame place, may ftrike this letter weakly ; but 

 when the letter M is brought under the hammer, the upper part of its head being much lefs. 

 elevated than that of the letter /', will receive a much ftronger blow. The impreflions of the 

 letters M and i will, therefore, always be equally deep, if the heads of the punches be once 

 properly fixed by experiment. 



Though I have already obferved, that the preffure in this machine is given by means of a 

 fcrcBTj I fhould certainly have ufed the hammer, if it were not for the inconvenience arifing 



from 

 f ■ 



