e sidereal heavens.

In the reflecting telescope, however, there are necessary limitations.
Before the middle of this century, it was known that the future of
astronomy depended upon the refracting lens, and not on the speculum.
The latter, in the hands of the two Herschels and Rosse, had reached
its utmost limits--as is shown by the fact that to this day the Rosse
telescope is the largest of its kind in the world.

Meanwhile the production of refracting telescopes made but slow
progress. As late as 1836 the largest instrument of this kind in the
world was the eleven-inch telescope of the observatory at Munich. The
next in importance was a nine and a half-inch instrument at Dorpat, in
Russia. This was the telescope through which the astronomer Struve
made his earlier studies and discoveries. His field of observation was
for the most part the fixed and double stars. At this time the largest
instrument in the United States was the five-inch refractor of Yale
College. Soon afterward, namely, in 1840, the observatory at
Philadelphia was supplied with a six-inch refracting telescope from
Munich.

German makers were now in the lead, and it was not long until a Munich
instrument having a lens of eleven inches diameter was imported for
the Mitchell Observatory on Mount Adams, overlooking Cincinnati. About
the same time a similar instrument of nine and a half inches aperture
was imported for the National Observatory at Washington. To this
period also belongs the construction of the Cambridge Observatory,
with its fifteen-inch refracting telescope. Another of the same size
was produced for the Royal Observatory at Pulkova, Russia. This was in
1839; and that instrument and the telescope at Cambridge were then the
largest of their kind in the world.

The history of the telescope-making in America properly begins with
Alvan Clark, Sr., of Cambridgeport, Massachusetts. It was in 1846 that
he produced his first telescope. Of this he made the lens, and such
was the excellence of his work that he soon became famous, to the
degree that the importation of foreign telescopes virtually ceased in
the United States. Nor was it long until foreign orders began to
arrive for the refracting lenses of Alvan Clark & Sons. The fame of
this firm went out through all the world, and by the beginning of the
last quarter of the century the Clark instruments were regarded as the
finest ever produced.

We cannot here refer to more than a few of the p