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lens in then ground down and polished suffi-

ciently to test its homogeneity and purity of it

proves satisfactory in these particulars it is there

finished. The difficulty in the way of success

his in this if there is a line of striae a quarter of

an inch long or a speck the size of a small spot

so far beneath the outer surface of the disk that it

cannot be ground out, it isa failure. Nine

hundred and ninety nine thousandths of the glass

may be perfect, if the remaining one thousandth

is defective it spoils the whole. Mr. [Feil?] has

cast [pane?] glass enough, in the 19 experiments,

to have made a dozen perfect lenses if he could

have separated it from these -as to size-helping

is defects. In pouring the [motled?] glass into an

enclosed space, like a mould, there is no way