6i2 THE POPULAR SCIENCE MONTHLY. 



flattened into something the shape of an enormous decanter. The 

 bottom is very flat, and has the bullion-point exactly in the cen- 

 ter. The pipe and its ungainly burden are now permitted to rest 

 horizontally on two iron supports. In the mean time a second 

 workman has gathered a small lump of glass on the end of his 

 iron rod, or " ponty," and by pressing it against an iron point 

 forms it into the shape of a tiny cup. This is fitted over the bull- 

 ion-point of the glass, and, as they are both hot, soon becomes 

 firmly attached to it. The glass has now two handles, but one of 

 these, the blow-pipe, is speedily separated from it by means of a 

 sharp blow. The open neck which is thus exposed is known, in 

 the glass-maker's parlance, as the " nose." It gives its name to 

 the furnace where it is subsequently reheated. During this oper- 

 ation the ponty is constantly and rapidly revolved. The nose 

 gradually expands under the combined action of heat and centrif- 

 ugal force. The oj)ening grows larger and larger until the glass 

 assumes the shape of a typical crown. This appearance, however, 

 remains but an instant. One sees in its place a brilliant circular 

 plate of glass whose shape is only maintained by continuing the 

 rotation of the ponty until the plate, or table, as it is now called, 

 can be placed upon a flat support. The ponty is then detached 

 from the bullion-point by means of shears. The mark that is left 

 is known as the bull's-eye. The tables vary in size from a few 

 inches in diameter up to six feet, but this latter dimension is ex- 

 treme. After annealing they are cut into panes by means of a 

 diamond. The loss involved in the operation more than counter- 

 balances the admirable brilliancy of the material. At the present 

 time, the circular tables, just as they come from the annealing 

 oven, are being used in decorative windows with the most excel- 

 lent effect. Frequently the glass is tinted, or else it is left color- 

 less itself, and the bull's-eye is either shaded or opalescent. 



The window-pane of the rich is commonly plate glass. Of 

 the three varieties, this is by far the most desirable in every- 

 thing except, it must be added, the price. Though similar in com- 

 position to the sheet and the crown glass, its fabrication is carried 

 out upon a totally different principle. Instead of being, like them, 

 the result of the blower's breath, the plate glass is cast into a flat 

 sheet and then ground and polished, a process of manufacture 

 which at once accounts for its expensiveness. The best practice 

 to be seen anywhere in America, if not in the world, is at Creigh- 

 ton, some twenty miles north of Pittsburgh. It is near the well- 

 known natural-gas district of Tarentum. There are a number of 

 large establishments in this country where plate glass is manu- 

 factured, but the Creighton plant enjoys the reputation of pos- 

 sessing the most favorable economic conditions as well as the best 

 equipment. 



