DUCTILITY of gla48. We all know, that when well penetrated with the heat of the fire the workman can figure and manage glass like soft wax ; but what is most remarkable, it may be drawn, er spun out, into threads exceedingly long and fine. Our ordinary spinners do not form their threads of silk, flax, or the like; with half the ease and expedition as the glass-spinners do threads of this brittle matter. We have some of them used in plumes, for children's heads, and divers other works, much finer than any hair, and which bend and wave like hair with every wind. Nothing is more simple and easy than the method of making them. There are two workmen employed ; the first holds one end of a piece of glass over the flame of a lamp, and when the heat has softened.it, a se cond operator applies a glass hook to the metal thus in fusion ; and withdraw ing the hook again, it brings with it a thread of glass, which still adheres to the mass : then, fitting his hook on the circumference Of a wheel about two feet and a half in diameter, he turns the wheel as fast as he pleases ; which, drawing out the thread, winds it on its run, till, after a certain number of revo lutions, it is covered with a skein of glass thread. The mass in fusion over the lamp diminishes insensibly, being wound out like a clue of silk upon the wheel ; and the parts, as they recede from the flame, cooling, become more coherent to those next to them, and this by degrees : the parts nearest the fire are always the least coherent, and, of consequence, must give way to the ef fort the rest make to draw them towards the wheel. The circumference of these
threads is usually a flat oval, being three or fonr times as broad as. thick : some of them seem scarcely bigger than the thread of a silk-worm, and are surpris-, ingly flexible. If the two ends of such threads are knotted together, they may be drawn and bent, till the aperture, or space in the middle of the knot, does not exceed one fourth of a line, or one forty eighth of an inch in diameter. Hence M. Reaumur advances, that the flexibili ty of glass increases in proportion to the fineness of the threads ; and that, proba bly, had we but the art of drawing threads as fine as a spider's web, we might weave stuffs and cloths of them for wear. Ac cordingly, he made some experiments this way ; and found that he could make threads fine enough, viz. as fine, in his judgment, as spider's thread, but he could never make them long enough to do any thing with them.