OF THE UNITED STATES. 373 



mas Jones, who made several of the instruments here de- 

 scribed, to make his dividing engine upon the principles 

 \vl)ich I indicated. 



Wiien the instrument comes from the hands of tlie first 

 workman, it is technically said to be tight, or fitted so as to 

 admit little or no motion of its axis. Then the circle intend- 

 ed to be divided, with its axis screwed to it, is i)ut in a lathe 

 to receive the last adjusting turning, lioth witli respect to the 

 axis and the plane of the circle. For this pur|)ose, it must 

 turn upon two points making part of the protracted axis. 

 As it would not turn sufficiently concentric in any common 

 lathe arrangement with chucks, a temporary |)ulley is fixed to 

 some convenient part, for the cords of the wheel to run in. 



The motion should be slow and steady, to avoid all vacil- 

 lation and swinging. Therefore tiie wheel is small, com- 

 monly one of those used with the hand lathe, and it is turned 

 regularly by a separate person by hand. 



When the axis and the plane of the circle arc thus finally 

 turned true, and before any thing is changed in the arrange- 

 ments, those circles, between which the divisions are to be 

 drawn, are immediately turned upon the plane of tlie instru- 

 ment, by the pressure of a fine point held in a position in- 

 clined to its motion, at about an angle of ten degrees, so that 

 no actual cuttitig takes place. 'I'hese circles are perfectly 

 concentric with the axis, and aro described better on a silver 

 arch than one of brass, on account of it's mure uniform tex- 

 ture and the ease with which it receives such an impression. 



The instrument being now taken from tlic lathe, the socket 

 of the axis, finished in the same manner, is rubbed upon it 

 with emery and oil, by a kind of screwing motion, untd an 

 easy and even motion is olMained. This turning following 

 always the conical surfaces by close contact, has no sensible 

 tendency to chance the centre. 



The present construction of the Fnglish dividing engines 

 requires an operation which makes the centre of the division 

 depend on the motion of the axis. It is necessary to take 



