3 J4 - On the improved Divid'mg Engine. 



observations and erroneous conceptions which appeared in 

 No. 30 of that work, relating to your Dividing Engine. 

 This learned critic I believe is determined, right or wrong, 

 to have the last word ; and I am also determined, after a 

 few remarks, to give him no further interruption. I well 

 know that I have no skill in book-making. What I have 

 said on your machine was my first essay, for which I am 

 accused of arrogance, confused and obscure explanation, 

 &c. Now, as that is the case, I may as well add a little 

 more to it, by declaring that I think my judgement in book- 

 making, so far as machinery used in the mathematical line 

 is concerned, is at least equal to that of my accusers, — pro- 

 bably, pretty much upon a par. 



In the first place, no other part of your Dividing Engine 

 ■was offered to the Society of Arts, for their consideration, 

 but a model of that on which the teeth are cut, and that 

 was merely to give some idea of a new plan, for producing a 

 certain number of equal tceih round a circle, with more ac- 

 curacy than had yet been done. The discussion therefore 

 rested solely on this one point, and was ultimately given in 

 your favour, and for the communication, the Society of Arts 

 have thought proper to honour you with the gold medal. 



After'all this, the Editor of the Retrospect seems still 

 disposed to cavil, and will not admit of any merit in your 

 invention. The reason I believe is this, that he does not 

 perfectly understand it. He is, probably, ignorant that on 

 your plan there are two rings in use, of the same diameter 

 and thickness, with an equal number of teeth in each, the 

 upper one moveable and the other fixed, perfectly concen- 

 tric to each other, and also to the centre of the machine 

 from which they move, — and so contrived, that when the 

 two rings are brought into contact and fastened together, 

 they appear as one only. In this state the racking is to 

 comaience, and it is to be carried on to about half the 

 depth, on Kamsden's plan, (which I would then abandon). 

 Perhaps lliere nuy now exist an error of y-^L^th part of aa 

 inch, which is a great deal. No matter if it was ten times 

 more. Yourplar., which now is to take place of cutting and 

 shifting as described in my last, will soon reduce it to no- 

 thing, and the operator may cut away, and look out at the 

 window almost all the time, and find that all his work has 

 been still going on right. 



Merely saying it is sa, because it is so, will not, I find, 

 satisfy every body : absolute geometrical demonstration is 

 the demand. The whole of the operation in this case is 

 purely mechanical, and a very fortuiiate one it is. 



Respectixig 



