On dividing Instmments,. . gj 



the figure, must hUo be fixed to the tnain plate of fio;. i, as 

 near to the tomicr as possible, but viewing one of tne divi- 

 sions on i.he roller. With a due attention to each micro- 

 scope, it will now be seen to tlic greatest exactness when, 

 by raising or depressing the roller, its commensurate diame- 

 ter is touuU. 



Fig. 3 is a rcpresc-tation of the apparatus for transferring 

 the divisions of_ the roller to the circle. It consists of two 

 sleiulcr*bars, which, being seen edcjewise in the tigure, have 

 only the appearance of narrow lines; but, when looked at 

 Irom above, they resemble the form of the letter A. They 

 are I'astened to the main frame, as at W and Z, bv short 

 pillars, havina; also the off leg of the angle secured in the 

 same manner, Y is a fine conical steel point for inakinij the 

 dots, and X is a feeler, whereby tlie point Yniav be pressed 

 down with a uniform i'orce, which force may be adiusted, 

 by bendina; the end of the bar just above tlie point, "so as to 

 make the dots of the proper size. The point Y yields most 

 readily ro a perj)e!ulicular action; butisamjily secured against 

 any eccentric or lateral deviation. 



The apparatus, so far described, is complete for laving 

 oij^ foundation, i.e. making 256 primary dots ; no matter 

 whether with perfect truth, or not, as was said respecting the 

 divisions of the roller; precision in either is not to be ex- 

 pected, nor wished ; but it isof soaie importance, that they 

 should be all of the same size, concentric, small, and round. 

 They should occupv a position very near the extreme border 

 of the circle, as well to give them the greatest radius pos- 

 sible, as that there should be room for the stationary mi- 

 croscope and ottje mechanism, which will be described 

 herealter. 



It mtist be noticed, that there is a clamp and adjustln"- 

 screw attached to the main plate of (ig. l ; but, as it difiers 

 in no respect from the usual contrivances for quick and slow 

 iDotion, it has been judged unnecessary to incumber the 

 drawing with it. 



Nkv, the roller havinir been adjusted, with one micro- 

 scope H upon its proper dot on the circle, and the other mi- 

 croscope at the lirst division on the roller; place the appa- 

 ratus of tig. 3 so that the dotting point Y may stnul dw-ecllv 

 over the place wliich is designed for the bcirinuinirof ihedi- 

 visior\s. in this |)osition of things, let the feeler X be pressed 

 dowti, until its lower end comes in contact with the circle; 

 this will carry down the point, and make the first imprcs- 

 bion, or primary dot, upon the circle ; unclamp the a|>pa- 

 ratus, and carry il IbrAards by hand^ until another division 



of 



