VOL. XXXVI.] PHILOSOPHICAL TRANSACTIONS. 401 



he placed the nail upright, with its point downward, and so rubbed off the 

 strokes of the file. He then rubbed it a little on a piece of leather. 



6. He prepared iron bars of different lengths after the following manner : he 

 made each end in the shape of the lower frustum of a pyramid, cut transverse 

 to its axis about the middle, or a little higher up. Then he filed the ends of 

 the bar as plain and perpendicular to its axis as he could, and polished them 

 with a hone, &c. as he did the nails. See fig. 11, pi. 10. 



7. One of the needles he used untouched, for trying experiments, was made 

 thus: he took, some iron wire, about the size of a small knitting needle, and 

 about 24^ inches in length. With a hammer he made it just flat enough in the 

 middle, to be able to fix the point of a punch pointed, to as true a cone as he 

 could; in the middle of the wire he punched a hole at least half way through 

 its thickness, and wrought the hole with a drill, pointed like the punch, that it 

 might be truly round, and cleansed off the asperity which the punch and drill 

 had raised round the hole, lest it should injure the top of the pin when placed 

 on it. Then he bended it in the form of fig. 1 1, taking care to bend it the 

 right way, that the hole might be on the under side. He then marked one 

 end, by flatting it a little with a hammer, that it might be known from the 

 other. Then placing it on a sharp pin, to find which end was heaviest, he 

 made both alike in weight, and deprived it of all fixed magnetism. Then he 

 brought it again to as true a poise as could be, by rubbing the heaviest end on 

 a whetstone, and not a file, which might give it magnetism again. He fitted a 

 pin for it of brass wire, full as small as the middle strings of a spinnet, making 

 the point very thin and round, as well as sharp, and observed it frequently with 

 a lens of 1 inches focus; and if it appeared flat, he mended it on a hone, and 

 took great care in putting on the needle, not to hurt the tender point of the 

 pin. He put a glass over it, to keep off all manner of fanning by the air, the 

 least degree of which would spoil the experiments. 



8. A second needle, which he thought better than the former, he made thus: 

 in the middle of such a piece of wire as the former was made of, he wrought 

 a hole perpendicularly through it, and as small as any of those drilled through 

 the pillars of a watch, if not smaller. And having bended the wire in the form 

 of fig. 13, he marked one end, and drove into the hole a small brass pin fitted 

 to it, which was very round and sharp at the point, which rested on a deep 

 plano-concave lens of glass well polished. He fitted a box for it, with a glass 

 over it, which was fastened with a ring of brass wire, as the glasses of tele- 

 scopes are, to keep out the air. The glass concave was fixed in the large end 

 of a thin brass ferule, just fit for it; and the small end of the ferule was fixed 

 in a hole, made for it in the middle of the bottom of the box ; lie also put a 



VOL, VII. 3 F 



