On examining the records of these practical modes of obtaining the best achromatic Flint Glass, it will be found that our philosophic countryman, Dr. Faraday, (the plan of Guinand being then a secret,) suggested the same idea of stirring, which was carried out successfully in the heavy Glass he manufactured. This was composed of—

His Glass required but a red heat for fusion, thereby offering facilities for minute agitating operations. Although it is not calculated for permanence or general use, its manufacture developed the fact, that the destruction of striæ is more dependent upon mechanical than chemical appliances; and that Dr. Faraday's conclusion and those of M. Bontemps and Guinand, jun., were identical in principle. The question may be asked, Why should there be difficulty in obtaining good achromatic flint Glass? There would be none, (is the reply,) if a manufacturer could anticipate a fair remunerative price and demand, after having succeeded in obtaining the quality. Probably, he could only sell 600 cwt. per annum, even were he to supply all the opticians in Great Britain at ten times the price of ordinary Flint Glass, which would scarcely be remunerative, whether he manufactured in one of the pots of a ten-pot furnace, containing each fifteen or eighteen cwt.; or upon a smaller scale, in