of astronomy are, for the most part, made with the first class of
instruments; its practical results wrought out by the second.

3d. The third class contains the clock, with its subsidiary apparatus,
for measuring the time and making its subdivisions with the greatest
possible accuracy; indispensable auxiliary of all the instruments, by
which the positions and motions of the heavenly bodies are observed, and
measured, and recorded.


THE TELESCOPE.

The telescope may be likened to a wondrous cyclopean eye, endued with
superhuman power, by which the astronomer extends the reach of his
vision to the further heavens, and surveys galaxies and universes
compared with which the solar system is but an atom floating in the air.
The transit may be compared to the measuring rod which he lays from
planet to planet, and from star to star, to ascertain and mark off the
heavenly spaces, and transfer them to his note-book; the clock is that
marvelous apparatus by which he equalizes and divides into nicely
measured parts a portion of that unconceived infinity of duration,
without beginning and without end, in which all existence floats as on a
shoreless and bottomless sea.

In the contrivance and the execution of these instruments, the utmost
stretch of inventive skill and mechanical ingenuity has been put forth.
To such perfection have they been carried, that a single second of
magnitude or space is rendered a distinctly visible and appreciable
quantity. "The arc of a circle," says Sir J. Herschell, "subtended by
one second, is less than the 200,000th part of the radius, so that on a