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tried in vain to remove it by very long fusion and fierce fire. Others
have found this by experience not to correct, but to augment the evil.
Mr. Keir is of the opinion that some new composition
must be discovered, which, along with a sufficient refractive power, shall
possess a greater uniformity of texture.|
Since then, it is certain some improvement has
been made in the composition for lenses. In an English paper we find
the following:-- "One of the most remarkable optical lenses of modern
manufacture is that produced by Messrs. Chance,
English manufacturers, being an attempt by them to improve the manufacture
of glass for optical purposes. The diameter is twenty-nine inches, and
it is two inches and a quarter thick. It is really not a lens, but a
plain disk intended for a lens, should its quality be sufficiently fine.
The weight is about two hundred pounds. This piece of glass was inspected,
on its first public exhibition, by eminent scientific judges. It was
by them examined edgewise, transversely, and obliquely; it was viewed
by daylight and by candle-light; it was tested by the polariscope and by
other means; and after having been thus subjected to a severe ordeal, it
was pronounced to be the largest and finest known specimen of the kind."