4$ PHILOSOPHICAL TRANSACTIONS. [aNNO 1780. 



then cut off, from the whole length, somewhat better than a 6th part, the whole 

 being sufficiently reduced to a thickness by the rollers. Perhaps no way will be 

 more ready and convenient to get such a long strip of brass reduced to an equal 

 breadth, than the method prescribed by Hindley; viz. by turning it on the chock 

 prepared; but I would not make it wider on one side than the other, like the 

 hoop of a cask, as he describes, but exactly to fit the chock, when truly cylin- 

 dric; for the internal elasticity of the brass, in so great a length, will be very 

 sufficient for fitting it on tight enough, without any tapering. This I will now 

 suppose done; and a pair of steel chaps, as described by Hindley, to be also 

 prepared, and ready for grinding; which, by such a careful admeasurement as 

 can easily be made, will give the length of the hoop sufficiently near, on its first 

 preparation. 



Ale t hod of forming a pair of straps as a check to the divisions. — ^The part first 

 cut off must be again cut into 2 equal parts in length; which, for distinction 

 sake, I will call the straps; and which are to serve as checks to every 6oth and 

 every 1 20th division of the circle. A steel plate, of about half an inch in breadth, 

 the same thickness as the straps, and in length equal to the breadth of the hoop 

 plate, must be soldered with silver solder to one end of each of the straps, by 

 which means their length will be increased half an inch by the steel. A hole 

 must then be made through each steel plate, of the same size as those through 

 the chaps, and answerable to the middle of the straps; but so near the border 

 of the steel, that when the chaps are put on, and adapted to the steel hole, the 

 next hole will fall through the brass. The steel plates must then be hardened; 

 and a pin being put through the two holes and the two plates, these must be 

 wrought to a right line in contiguity to each other; by this means the 

 straight edge of each of the straps will be reduced to the same distance from 

 the steel hole: the hard steel edges may be rectified by the grindstone, if 

 necessary. 



This being done, not only the holes in the chaps, but the holes in the two 

 steel plates, applied to each other, like the two sides of the chaps, must be 

 respectively ground together; not with a taper pin, as prescribed by Hindley; but 

 so as not only to be cylindrical, but that the same cylindrical pin shall equally fit 

 them all, and leave them smooth and polished; which is a process no ways diffi- 

 cult to a curious artist, and of which therefore a minute description is unneces- 

 sary. The chaps being then put on one of the straps, with its straight edge 

 uppermost, and a pin put through the holes on the left-hand, and through the 

 steel hole in the strap under operation, the chaps must be set upright, so that 

 the line joining the centres of the holes shall be parallel to the upper edge of 

 the strap ; the brass plate, mentioned by Hindley, between the chaps, as a guide 



