they were superior to the telescope on account of their freedom from
refraction.

But as soon as the principle by which distant objects could,
apparently, be brought nearer the eye became known and its value
recognized by philosophers, telescopes ceased to be regarded as toys,
and underwent material improvements in the hands of such men as
Galilei, and, later, even of Kepler himself, Cassini, Huyghens, and
others. Galilei's first telescope magnified but three times, and his
best not much above thirty times. If I comprehend aright what has been
written upon the subject, I am justified in saying that this little
instrument in my hand, with an aperture of one inch and one-quarter,
and a focus, with an astronomical eye-piece, of about ten inches, is a
better magnifier than was Galilei's best. With it I can see the moons
of Jupiter, some spots on the sun, the phases of Venus, the
composition, in some places, of the Milky Way, the seas, the valleys,
the mountains, and, when in bold relief upon the terminator, even some
of the craters and cones of the moon. Indeed, I am of opinion I can
see even more than he could, for I can readily make out 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