6io 'THE POPULAR SCIENCE MONTHLY. 



is accomplished is one of the triumphs of modern glass-making. 

 In this department particularly, the merits of natural gas are each 

 day more apparent. The hearth of the laying-in furnace is circu- 

 lar, and is divided into a number of sectors by fire-clay bridges. 

 It is made movable about a vertical axis. As it rotates, the dif- 

 ferent sectors of the hearth pass through as many separate com- 

 partments of the furnace, the temperature of which may be varied 

 at pleasure. The first compartment, the laying-in oven, is only 

 moderately warm, and permits the glass cylinder to become grad- 

 ually heated. It is then carried by a partial rotation of the 

 hearth into the next compartment, the laying-out oven, where the 

 heat is sufficient to make the glass plastic. A large, flat stone 

 occupies each hearth-section and forms the ironing-board upon 

 which the cylinders of glass are to be smoothed. In the laying- 

 out oven, the crack in the cylinder is brought uppermost. Under 

 the influence of the heat the glass gradually unfolds, until it lies 

 open on the stone like a sheet of rumpled paper. In the succeed- 

 ing compartment — the flattening oven — the plastic sheet is made 

 perfectly smooth and flat by means of a moist block of wood on 

 the end of a long iron rod. The cylinder has now disappeared, 

 and in its place there is a pane of red-hot glass. One more turn 

 of the hearth carries the glass into the compartment known as the 

 dumb oven, where it gradually cools. It is then brought, by a 

 final movement of the hearth, to the entrance of the annealing 

 leer. One whole rotation has now been accomplished, and the cir- 

 cuit is complete. Meanwhile other cylinders have been put into 

 the furnace and are in different stages of the flattening process. 



The operation of the furnace is continuous, and speedily trans- 

 forms the cylinder into a smooth sheet. But still it is not ready 

 for use. Were the glass removed to the air immediately, it would 

 be much too brittle for service. It must first go through the pro- 

 cess of annealing, or gradual cooling, before it can possess any 

 durability. In the improved " rod leer " the hot glass is received 

 at one end of a long brick chamber, and in thirty or forty min- 

 utes it is automatically discharged at the other end, nearly or 

 quite cold. Where gas is used, the glass, just as it comes from 

 the leer, is beautifully clear and brilliant. It could scarcely be 

 more so had it been washed with hot water and dried with linen 

 — the process, we believe, by which madam, our hostess, secures 

 such a glittering display on her table. The sheets are at once cut 

 into proper sizes and stored away in suitable wooden frames. 

 The process of manufacture is completed, and only the service of 

 the glazier is needed to put the pane in place, and so inaugurate 

 its luminous mission. 



Strange fancies attend the visitor as he wanders through the 

 silent warehouse. He loses himself amid the possible pictures 



