The operation is conducted by three workmen. The first takes the blowing pipe 7, and after heating it to a red heat at the mouth of the furnace, dips it into the pot of melted glass, at the same time turning it round, that it may take up the glass, which has then much the consist ence of turpentine ; in the quantity of metal he is guided by experience, and must proportion it to the size of the ves sel to be blown ; lie then brings it from the furnace to the stool, fig. 9, and rolls the lump of glass upon it to bring it to a round form,a ft er which he blows through the pipe, resting the glass upon the iron plate f behind the stool, as in the figure, and rolling it backwards and forwards. The blowing makes the glass hollow, and he has several methods of bringing it to a proper shape to be worked ; by simply blowing, it would assume a figure nearly globular; if he wants it any bigger, in the equatorial diametergg, fig. 11, he lays the pipe on a hook driven in the side of the stool, and turns it round very quickly ; the centrifugal force soon enlarges it in the equator. If, on the other hand, he wishes to lengthen its polar diameter, he holds the pipe perpendicular, the glass hanging downwards, its weight lengthen ing it, and to shorten the polar diameter, he holds the pipe upright, the glass at the top by blowing through the, pipe the ca pacity is increased, and the thickness of the glass of the vessel diminished.
time now suppose, that by a very dex terous application of the above methods the workman has brought it to the shape of fig. 11; he now carries it to the mouth of the furnace, and holds it in to get a fresh heat, (for by this time it is become too stiff to work easily) taking care to turn it round slowly, that it may not alter its figure. The vessel in this stage is deli vered to the second, or principal work man, the other two being only assistants ; he is seated upon the stool, figs. 1 and 2, and lays the blowing pipe, with the glass at its end, across its arm a b, and with his left hand rolls the pipe along the arms; turning the glass and pipe round at the same time ; in his right hand he holds the pliers, fig. 3, whose blades are rubbed over with a small piece of bees'-wax, and as the glass turns round presses the blade of the shears against it, following it with the shears as it rolls, at the end or side, as occasion requires, until he has brought it to the proper size, which he determines by the compasses, fig. 4, though not ma terially altering its figure, the first work man kneeling on the ground and blowing with his mouth at the end of the pipe, which hangs over the arm b, when di rected by his principal. The third work man now produces the small rod, fig. 8, which is dipped into the melting pot, to take up a small piece of metal to serve as cement ; the end of this rod lie applies to the centre of the glass, just opposite the blowing pipe, the principal workman di recting it, by holding its end between his pliers, the rod by the small piece of glass on its end immediately sticks to the glass vessel, and the third workman draws it away, both workmen turning their rods round; but in contrary directions ; this operation forms a short tube on the end, as in fig 12. The principal workman then
takes the short tube at i, between the blades of a pair of pliers, exactly like the others, but which are not covered with bees'-wax ; the cold of these pliers in stantly cracks the glass all round, and a very slight jerk struck upon the rod 8 breaks it off. A hole is now made in the end of the glass; which is enlarged by the pliers while the glass is turned, as in fig. 13, until the neck is brought to the pro per size and length to fit the brass cap, as before described, and the inferior half of the lamp is brought to its shape and size in the same manner.
In order to form the upper half, the third workman has in the meantime been preparing a round lump of glass K, fig. 14, on the end of one of the rods, fig. 8, this he applies hot to the end of the neck, it being guided by the principal workman, and it immediately holds tight, he then breaks offthe other neck at 7, by the cold pliers, and thus separates it from the blowing pipe.
The glass is now heated a third time, and brought from the furnace in the state, fig. 15, to the principal workman, who enlarges the small orifice at the end by turning it round, and holding the pliers against it, until he enlarges it, as in fig. 16, to the shape of fig. 10 ; it is now finished, and the third workman takes it to a stool strewed over with small coals, he rests the rod upon the edge of the stool, and with the file, fig. 6, files the joint at the bot tom neck, which soon breaks off, and the lamp falls upon the coals, the distance be ing so very small, as to be in no danger of breaking; a boy now puts the end of a long stick into the open mouth of the glass, and thus carries it up the steps be fore described, places it in the annealing oven, where it remains some hours ; when taken out it must be tooled gradu ally, and is fit for sale.
In the history of glass, there is a fact deserving record ; it is related by Pliny, that the discovery was owing to the following accident. Some merchants, with soda as part of their freight, had cast an chor at the mouth of the river Belus, in Pheenicia, and were dressingtheir dinner on the sand, making use of large lumps of the soda as supports for their kettles. The heat of the fire melted the soda, and the siliceous earth together ; the result was glass. The hint was not lost, and a manufacture in that trading country was instantly established, and to this place it was for a long time contined. Glass was undoubtedly made in great perfection among the ancients. In their accounts, we read of drinking-glasses, glass prisms, and coloured glasses of various kinds. Glass was first used for windows in the Jd century of the Christian ara, but it did not come into common use till very long after this.