OF COPYING.

77

(110.) IFire drawing .—The metal to be convertedinto wire is made of a cylindrical form, and drawnforcibly through circular holes in plates of steel: ateach passage it becomes smaller; and when finished,its section at any point is a precise copy of the lasthole through which it passed. Upon the larger kindsof wire, fine lines may frequently be traced, runninglongitudinally ; these arise from a slight imperfectionin the holes of the draw-plates. For many purposesof the arts, wire, the section of which is squareor half round, is required: the same method ofmaking it is pursued, except that the holes throughwhich it is drawn are in such cases themselvessquare, or half round, or of whatever other form thewire is required to be. A species of wire is made,the section of which resembles a star with from six totwelve rays ; this is called pinion wire, and is usedby the clock-makers. They file away all the raysfrom a short piece, except from about half an inchnear one end : this becomes a pinion for a clock; andthe leaves or teeth, having passed through the draw-plate, are already burnished and finished.

(111.) Tube drawing .—The art of forming tubesof uniform diameter is nearly similar in its mode ofexecution to wire drawing. After the sheet-brasshas been bent round and soldered so as to forma hollow cylinder, if the outside diameter is thatwhich is required to be uniform, it is drawn througha succession of holes, as in wire drawing. If theinside diameter is to be uniform, a succession ofsteel cylinders, called triblets, are drawn through thebrass tube. In making tubes for telescopes, it isnecessary that both the inside and outside should