66 Detail of the ConJlruUion af 



Description of the Machine for Engraving, 



This machine confifts of two brafs wheels, placed on the lame axis above each other, and 

 feparated by a number of pillars, each two inches in length (Plate III). Thefe two wheels, 

 with the interval which feparates them, are equivalent toa lingle wheel about three inches thiclc. 

 la order, therefore, to fimplify my defcription, I (hall confider them as a fingle wheel which 

 mpves freely on its axis. 



This wheel is perforated near its circumference with a number of fquare holes, which are 

 the fheaths or fockcts through which a like number of fteel punches, of the fame {hape, are 

 inferted, and are capable of moving up and down. They are very well fitted, and from this cir- 

 cumftance, as well as the thicknefs of the double wheel, they have no Ihake, or fide motion, 

 independent of the motion of the wheel itfelf. Every punch is urged upwards by a feparatc 

 fpring, in fuch a manner, that the wheel armed with its charadters, or fteel types (the lower 

 faces of the punches being cut into the figures of the feveral letters), may turn freely on its 

 axis ; and if it be moved, the feveral punches will pafs in fucceflion beneath an upright fcrew, 

 for pre/Ture, The fcrew is fixed in a very firm and folid frame, attached to the fupports of 

 the machine ;. and by this arrangement, a copper-plate, difpofed on the tabic, or bed of the 

 apparatus, will receive the imprelTion of all the punches in fucc-'Jion, as they may be brought 

 beneath the vertical preffing-fcrew, and fubjefted to its adtion. 



But as the prcfe is fixed, it would neceflarily follow that each fucceflive imprellion would, 

 in part, deftroy, or mutilate, the previous impreflions, unlefs the plate itfelf were moveable. 

 It therefore becomes necefi'ary that the plate fhould be moveable in two direflions ; the firft 

 to determine the interval between the letters and words, and form the lines ; anJthe other mo-^ 

 tion, which is more fimple, becaufe its quantity may remain the fame through the whole of X 

 book, ferves to give the interval between line and line, and to form the pages. 



It will eafily be conceived, that it would be a tedious operation to feek, upon the circiims- 

 ference of the wheel, each feveral charadter, as it might be required to come beneath the prefs, 

 becaufe it is necelTary to repeat this operation as many times as there are characters in a work. 

 1 have confiderably diminiihed the time and trouble of this operation, by fixing upon the axis 

 of the great wheel, which carries the punches, another fmall wheel, about four inches in diav 

 meter, the teeth of which a£t upon a rack, which carries a rule moving between two Aiders. 

 This rule, or ftraight line, will, therefore, reprefent the developement, or unfolding of the cir- 

 cumference of the wheel which caufes it to move, and will (hew the pofition of the great 

 wheel, which carries the punches. For thefe two wheels being concentric, the developement 

 of the fmall toothed wheel, of about two inches radius, will exhibit, in a fmall fpace (for ex- 

 ample, that of a foot), an accurate regifter of the relative pofitions of the punches, with 

 regard to the prefling-fcrew. To obtain this efFeft, nothing more is necelTary than to place a 

 fixed index oppofite the moveable rule, which laft is divided in the following manner: 



The punch on which the firft letter of the alphabet is engraved, muft be brought under the 



centre 



