52 PHILOSOPHICAL TRANSACTIONS. [anNO 1786. 



smooth taper pins are to be driven ; not with violence, but moderately, that no 

 sensible stretching of the solid parts may take place ; then cutting oft' and smooth- 

 ing the heads, shift the vises so as to receive another couple of holes, and a third 

 couple in the same end of the hoop ; and proceed progressively in the same man- 

 ner, from the middle to the other end of the rivet plate ; then gentiy separate the 

 internal brass mould with a thin knife, or such like instrument ; and cutting off^, 

 and very lightly rivetting the inner ends, proceed to fix the other rivet plate, in 

 the same manner, on the other side: by this means the hoop will be firmly joined 

 in the very position given it by the saddle plates and mould. These plates may 

 then be removed, the inside of the hoop cleared and smoothed, if necessary ; and 

 the outside will have the middle part clear where the divisions lie, and that with- 

 out sensible loss or gain in the juncture. 



Method of Transferring the Divisions of the Hoop to a Dividing Plate. — The 

 hoop being thus refitted for the chock, that should be turned down to leave a 

 shoulder on one side, that the hoop, now reduced to an equal breadth, may be 

 forced against it ; and the divisions, being equally distant from one of its edges, 

 will be all found in a circle, as if turned on it. It should be very carefully fitted 

 to the chock, that it may go on with a suflScient degree of tightness, and without 

 the necessity of much forcing ; and it will be no inconvenience now, if it goes on 

 a very slight degree of taper of the chock, as the internal spring of the materials 

 will easily accommodate it to this shape without any injury to its general truth : a 

 slight degree of a groove should be turned in the place where the divisions will 

 come, that any conical pin, that is to serve as an index, let drop into the divisions 

 or holes, may not, by reaching through this thin plate, abut on the wood, rather 

 than on the sides of the holes : and thus this hoop is made into a wheel of 1440 

 equal divisions, moveable round on its own axis, on which it was formed. 



Against the time that this is completed, there must be prepared a flat circular 

 plate or wheel of brass, the rim of which should be of about 3-i- inches breadth, 

 and about -^ of an inch in thickness when finished, to make a dividing plate ; the 

 external diameter of this is to be such, that when laid flat on the surface of the 

 mahogany platform, its extreme edge will exceed the diameter of the hoop by 

 about half an inch all round. There must also be prepared brass arms, suppose 

 8 in number, of an equal substance with the outer rim, and all connected with a 

 circular plate in the middle ; and, the whole of this work being framed beforehand, 

 is to be let on flat upon the mahogany platform ; whose face is supposed to be 

 turned truly flat, and sufficiently affixed with screws : in this situation, the out- 

 ward edge is to be turned, and the outward face of the rim turned fiat. The 

 centre plate, which may be about 12 inches diameter, is also to be turned as flat 

 as possible, and a centre hole, of about half an inch diameter, to be very care- 

 fully turned in it. 



