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wafte glafs falls in drops, and is ufed for the In proportion as the furfaces of the plates wearnext melting. The number of workmen re- down the fand is ufed fucceffively finer, beingquired for the whole procefs of calling is at previoufly lifted and forted for the purpofe. Inleaft twenty, each of which has his feparate em- general the workmen avoid rubbing two abfo-ployment. lutely rough furfaces on the other for fear that

The plate being call, the infpedlor examines the great jarring of the fridtion fliould producewhether there are any bubbles on any part of {hakes and flaws in the glafs, but a half groundthe furface, and if found, the plate is imme- plate is rubbed on a frelh furface and fo on fuc-diately cut up through them. The plate being ceflively.

now fo far cool as to be ItifFened is Hid by an When one fide of the plate is done, theiron inftrument from the calling table to the platter which cemented it is picked off, thecontiguous annealing oven previoufly well heat- plate turned, and the oppofite fide ground ined, and is carefully taken up and ranged pro- the fame manner. Towards the end of the-perly within it. Each oven will contain fix en- grinding the preffure is encreafed by loadingtire plates, and when full, all the openings are the upper plates with flat Hones of differentHopped with clay and the plates allowed to re- thickneffes. This procefs lafts about three days,main there for a fortnight to be thoroughly an- and great attention is paid to finilh them withnealed. furfaces perfectly flat and parallel, which is de-

When fit to be taken out of the annealing termined by the ruler and plumb-line. Theoven they are fent away to receive all the fub- ground furfaces are now uniformly worn byfequent operations of polilhing, filvering, &c. millions of fcratches, and therefore nearly opakebut firft their edges are cut fmooth and fquared. unlels held up to the light, but ftill very farThis is done by a rough diamond which is from having the requifite finenefs to receivepaffed along the furface of the glafs upon a the polifli. This further grinding is done byfquare ruler in the manner of glaziers, and emery of different degrees of finenefs, the pre-made to cut into the fubflance of the glafs to paration and forting of which is done in thea certain depth. The cut is then opened by following very Ample manner. A large quan-gently knocking with a final 1 hammer on the tity of rough emery is put into a veffel with-under fide of the glafs juft beneath, and the water and ftrongly ftirred about till the wholepiece comes off, and the roughneffes of the is mixed. But as emery is abfolutely infolubleedges are removed by pincers. The plate is in water the whole will again be depofited inthen finifhed as far as the glafs-houfe bufinefs fucceffive layers, the coarfefl particles finkingis concerned and is carefully removed to the firft, and the others afterwards in the i nverfewarehoufe. degree of their finenefs. By flanding about

The fubfequent operations of polifhing and twenty minutes and then pouring off the fu-filvering may here be added in a few words. 1 pernatant liquor, the latter bolds fufpended onlyThe plate is firft exactly fquared by the dia- the very fineft particles which again feparate bymond in the way- mentioned above, and mi- reft for a longer time. More water is then addedmutely examined as to any flaws or faults to the veflel, the emery (lined again, and nowwhich may- be found. The next ftep is to allowed to remain at reft only for fifteengrind off all the inequalities and roughneffes minutes, and the fupernatant turbid liquorof furface previous to the polifhing. This is again poured off. This furnifhes by reft andone on both fides by fand and water. For emery of the fecond degree of finenefs. Thethis the plate is laid on a thin plate of free- fame is repeated twice more at the differentflone or on a long wooden frame, of about times of about five minutes and half a minute,the fame fize with it and cemented flrongly by which two other forts are obtained. Thethereto by Paris plafter. Another plate is alfo wet emery from all thefe liquors is feparatelycemented in the fame manner and laid upon heated over a (love to evaporate the water, andthe lower plate, and wet land is interfperfed when nearly dry is made up into balls in whichbetween the two. The plates are then made flate it is diftributed to the workmen,to rub againft each fleadily and evenly by a The plates are then further ground on bothkind of hand mill, the wheel of which is fides with two or three emerys, beginning withworked by a man, or fometimes in large plates the coarfefl and are finifhed with great care,by two men, who can regulate the preffure of They are now perfectly even, with a deadeningone on the other as it may be judged proper, or opacity on their furface, but fo fine that uu

'Eacyclop. Mcth. Journ.and Polytech. pt.5,.