State of the Useful Arts. . 271 



luent of the tool to be pei-formed by any agent capable of exhi- 

 biting the required amount of physical power — yet the rapidity 

 of this advancement he must also regulate. 



That the slide-rest is capable of producingan increased amount 

 of certain kinds of work, will be allowed by all. .Thus, suppose 

 that we have to turn a vast number of plugs for stop-cocks- 

 The receptacles for these plugs have been all brotched out to one 

 size and one taper, by the use of one and the same brotching-tool. 

 To turn a plug by hand is difficult and tedious. The preser- 

 vation of a perfect straight line in the taper is impossible ; and 

 the regulation of the degree of taper a matter of repeated trial. 

 But with the slide-rest, the accuracy of lineation and the true 

 angle of obliquity are at once obtained ; and the rest once set, 

 nothing has to be attended to, save the giving of the proper dia- 

 meter to one or other end of the cone. In such a case as this the 

 amount of work produced by the same number of hands has 

 been augmented four, five, six, and even ten times ; nor is this 

 all ; the operations have been performed with prodigiously in- 

 creased precision ; so much so, that perhaps a thousand times 

 the time had been spent by the hand workman in the vain at- 

 tempt to rival it. 



Multitudes of examples of this kind occur in practice ; as in 

 the turning of the spindles and other parts of spinning machines, 

 where thousands of copies of the same form are needed ; and 

 where these copies must not merely look tolerably well, but where 

 they must be so exact that one may be placed instead of the 

 other. In such cases, I have said, nobody disputes the advan- 

 tage of the slide. It is where a single article has to be made that 

 it is supposed to be disadvantageous. Here the whole trouble 

 of adjusting falls on one piece of work, instead of being subdi^ 

 vided among hundreds. 



But what is really the case in hand-turning ? The drawing of 

 the intended article is laid down, and measurement after mea- 

 surement is made from it ; the callipers are applied repeatedly, 

 the aim of the turner being not to turn too much off, but to 

 bring, by repeated essays, the work to the required size and 

 form. The eye cannot transfer with certainty the dimensions 

 from the flat paper to the solid material, and hence a waste of 



