works on the subject telescopes as large as five inches or even five
and one-half inches are included in the description "common," but
instruments of such apertures are not so frequently met with in this
country as to justify the classing of them with smaller ones, and,
perhaps, for my purpose, it is well that such is the fact, for the
expense connected with the purchase of first rate telescopes increases
very rapidly in proportion to the size of the object glass, and soon
becomes a serious matter. Should ever the larger apertures become
numerous on this continent, let us hope it shall be found to have been
as one of the results of societies like this, striving to make more
popular the study of astronomy.

It is not by any means proposed to inflict upon you a history of the
telescope, but your indulgence is asked for a few moments while
reference is made to one or two matters connected with its invention,
or, rather, its accidental discovery and subsequent improvement.

The opening years of the seventeenth century found the world without a
telescope, or, at least, such an instrument as was adapted for
astronomical work. It is true that long years before, Arabian and some
other eastern astronomers, for the purpose, possibly, of enabling them
to concentrate their gaze upon celestial objects and follow their
motions, had been accustomed to use a kind of tube consisting of a
long cylinder without glasses of any kind and open at both ends. For
magnifying purposes, this tube was of no value. Still, it must have
been of some kind of service, or else the first telescopes, as
constructed by the spectacle makers, who had stumbled upon the
principle involved, were exceedingly sorry affairs, for, soon after
their introduction, the illustrious Kepler, in his work on "Optics,"
recommended the employment of plain apertures, without lenses, because