VOL. LXVII.] PHILOSOPHICAL TRANSACTIONS. 1 63 



of the brass tool either way, shifting the bruiser round its axis at about every 

 half dozen strokes. Also every now and then shift your own position, by walk- 

 ing round, and working at different sides of the brass tool; at times the strokes 

 sliould be carried round and round, but not much over the tool: in short, they 

 must be directed in such a way, and the whole grinding conducted in such a 

 manner and witli such equability, that every part of both tools may wear equally. 

 This habit of grinding, as well as the future one of polishing, will be soon 

 acquired. When you have wrought in this manner about a quarter of an hour 

 with the bruiser on the tool, it will be then necessary to change them, and, 

 placing the bruiser on its bottom, to work the convex tool on that in the same 

 manner. 



When by working in this equable manner, alternately with the bruiser and 

 tool, and occasionally adding fresh emery, you have nearly got out all the vestiges of 

 the turning tool, and brought them both nearly to a figure, it will be then time 

 to give the same form to the metal. This must be done by now and then grind- 

 ing it on the brass tool with the same kind of emery, taking care however, by 

 working the two former tools frequently together, to keep all 3 exactly in the 

 same curve. The best kind of handle for the metal is made of lead, a little 

 more than double its thickness, and somewhat less in diameter, of about 3 lb. 

 weight, with a hole in the middle (for reasons to be shown hereafter) a little 

 larger than that in the metal: this handle should be cemented on with pitch. The 

 upper edge of this weight must be rounded off, that the fingers may not be hurt; 

 and a groove, about the size of the little finger, be turned round just below it, 

 for more conveniently holding and taking the metal ofl^" the tools. 



The manner of Jignring the metal on the hones. — When the bruiser, brass 

 tool, and metal are all brought to the same figure, and have all a true good 

 surface, the next part of the process is to give a correct spherical figure, 

 and a fine face to the metal on the hones. It will be necessary to premise 

 hovever, that the hones should be placed in a vessel of water, with which 

 they should be quite covered for at least an hour before they are used, other- 

 wise they will be perpetually altering their figure when the metal comes to 

 be ground on them. The same precaution is also necessary, if you are called 

 off from the work while you are grinding the metal ; for if they be sufi^ered to 

 get dry, the same inconvenience will arise. 



In order to give a proper figure to the hones, and exactly suitable to that of 

 the brass tool, bruiser, and metal, when the hones are fixed down to tne block, 

 some common flour emery (unwashed) with a good deal of water, must be put 

 on them, and the bruiser being placed on the hones, and rubbed on them with a 

 few strokes and a light hand, the inequalities of the stone will be quickly worn 

 off; but as a great deal of mud will be suddenly generated, it must be Vvashed 



T •! 



