227 Mr Sang's Annual Report on the 



time, far more tedious than that spent in adjusting the cutter of 

 the shde-rest. And after all, unless it be an affair where pre- 

 cision is not aimed at, where delicacy of outline and of curva- 

 ture are all important, the finished hand-turning is any thing 

 but complete ; and smoothing papers have to be applied to per- 

 fect the surfaces. 



When three or four copies are needed, the hand-turner is 

 more at ease ; yet even his first copy occupies more time than 

 the original pi?ce; for now he has to give a much more com- 

 plete resemblance, as the eye detects much more easily a disa- 

 greement between two solids, than between a solid and its ortho- 

 graphic projection. The third, and fourth, and fifth perform- 

 ances, however, are gone through with great rapidity, and if many 

 copies be required, each may not average the third or fourth 

 part of the lime spent on the first. 



Contrast this process with the operation of the slide-rest. A 

 cut is made, and the dimensions of the material left ascertained 

 by the callipers; a simple subtraction tells how much more must 

 be taken off, and the divisions on the head of the leading screw 

 give at once the proper advance to the tool, so that the work is 

 made of the required size safely and directly. There need here 

 be no guessing as to how far we must go, no fear that the ma- 

 terial is destroyed by an over cut ; and in this way a drawing is 

 copied with a rapidity and safety that can hardly be equalled 

 by the best hand-turners. 



The only thing in which the slide-rest appears to fall decid- 

 edly short of the hand-tool is in the last delicate finish of a curv- 

 ed outline ; and there its inferiority is palpably apparent. Yet 

 in the formation of the approximate outline, it is not inferior to 

 the hand-tool ; and in the cases of brass or iron is perhaps supe- 

 rior to it. For the removal of the ridges left between the succes- 

 sive cuts, the hand must be employed, and not the hand mere!}'-, 

 but after it, grinding stones, and smoothing and polishing papers. 



The introduction of the slide-rest has brought into view sources 

 of inaccuracies in the turning-lathe, that before were hardly 

 dreamt of. 



The edge of the tool wears as the work goes on, and hence a 

 deviation from the trueform. Thus,in the example before cited of 

 turning stopcock plugs, the tool, after many cuts, has been worn 



