But at the same time I learned that the new
glass was very soft and difficult to polish, and also that it had to
be protected from the atmosphere, and further, that an English
optician had failed to construct an improved telescope objective from
it. I had ordered some samples of the glass, but never received any.
A few months ago, news from Europe reached this country that another
and seemingly more successful attempt had been made to produce glass
that would leave no secondary spectrum, and that Dr. Zeiss, the famous
Jena optician, had constructed some new improved objectives from it.
But the somewhat meager description of these objectives, as given by
an English microscopist, did not seem fit to excite much enthusiasm
here as to their superiority over what had already been done in this
country. Besides this, the report said that the new objectives were
five system, and also that extra eye-pieces had to be used with them.
I confess I am much inclined to attribute the optical improvement,
which, according to Dr. Abbe's own remark, is very little, more to the
fact that the objectives are five system than to the new glass used in
their construction.
After a close study of a descriptive list of the new glass, received a
week or two ago from the manufacturers, I find, to my great regret,
that this new glass seems to suffer from a similar weakness to that
made by the English firm twelve years ago; as all the numbers of the
list pointed out by the makers as having a greatly reduced secondary
spectrum are accompanied with the special remark "to be protected.
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