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making, for optical and other purposes, gave a short account 

 of them to the Academy. 



The improvements consist chiefly in — 



1st. The use of platina bottoms to earthen melting pots, 

 and heating these in improved furnaces from below, so as to 

 produce circulation in the fluid glass. 



£nd. In preserving the liquid glass from all contamina- 

 tion from without by " tears," &c. and from the dome of 

 the furnace, as well as from deoxidation of the lead salts by 

 contact of carbon. 



3rd. In an improved mode of cutting off, by a platina 

 blade, the upper portion of the fluid glass, without distur- 

 bance of the remainder ; thus separating the whole of the 

 impure dross at top, which was heretofore stirred down into 

 the mass just previous to casting. 



4th. In a beautiful and effective mode of removing the 

 air bubbles, or " seeds," as they are called, from the liquid 

 glass, by placing the ignited glass pot of liquid metal within 

 an exhausted receiver, so contrived that it can be rapidly 

 placed within, and withdrawn from the vacuum vessel. 



Mr. Mallet was not aware that as yet any specimen of 

 glass prepared by these improved processes had been wrought 

 for any optical purpose, the inventor's efforts having been as 

 yet principally directed to the manufacture of plate glass ; 

 but he considered that the practical nature of these improve- 

 ments, and their capability of being applied upon a large 

 scale, gave good hope of their extension to the making of 

 optical glasses also. 



Rev. Dr. Robinson made some remarks with reference to 

 Mr. Faraday's experiments on the manufacture of glass for 

 optical purposes, and described the processes adopted at 

 Munich in selecting the portions of glass of which lenses are 

 formed. 



