ut a considerable
portion of the Great Nebula in Orion, some double stars, and enough of
the Saturnian system to discern the disk of the planet and see that
there is something attached to its sides.

For nearly one hundred and fifty years all refracting telescopes
labored under one serious difficulty. The images formed by them were
more or less confused by rainbow tints, due to the bending, or
refracting, by the object glass of the rays of light. To overcome this
obstacle to clear vision, and also to secure magnification, the focal
lengths of the instruments were greatly extended. Telescopes 38, 50,
78, 130, 160, 210, 400, and even 600 feet long were constructed. I
can, however, find nothing on record indicating that the object
glasses of these enormously attenuated instruments ever exceeded in
diameter two and one-half inches. Yet, with unwieldy and ungainly
telescopes, nearly always defining badly, wonders were accomplished by
the painstaking and indomitable observers of the time.

In 1658, Huyghens, using a telescope twenty-three feet long and two
and one-third inches in diameter, with a power of 100, solved the
mystery of Saturn's rings, which had resisted all of Galilei's efforts
as well as his own with a shorter instrument, though he had discovered
Titan, Saturn's largest moon, and fixed correctly its period of
revolution at sixteen days. Fifteen years later, Ball, with a
telescope thirty-eight feet long, discovered the principal division in
the rings. Ten years still later, Cassini, with an instrument twenty
feet long and an object glass two and one-half inches in diameter,
rediscovered the division, which was named after him, rather than
after Ball, who had taken no pains to make widely known his discovery,
which, in the meantime, had been forgotten. Though we have no record,
there is no doubt that the lamented Horrocks and Crabtree, in England,
in 1639, with glasses no better than these, watched with exultant
emotions the first transit of Venus ever seen by human eyes.

In 1722, Bradley, with a telescope 2231/4 feet long, succeeded in
measuring the diameter of the same planet. Yet Grant assures us that,
in spite of all their difficulties, such was the industry of the
astronomers that when, at the commencement of this century, it became
possible to construct larger refracting telescopes, there was nothing
to be discovered that could have been discovered with the means at
their disposal. So far as we now know,