to the inch, for occasional use;
and a medium power--say forty to the inch--for general use. If you can
afford it, get a full battery of eyepieces--six or eight, or a
dozen--for experience shows that different objects require different
powers in order to be best seen, and, moreover, a slight change of power
is frequently a great relief to the eye.

There is one other thing of great importance to be considered in
purchasing a telescope--the mounting. If your glass is not well mounted
on a steady and easily managed stand, you might better have spent your
money for something more useful. I have endured hours of torment while
trying to see stars through a telescope that was shivering in the wind
and dancing to every motion of the bystanders, to say nothing of the
wriggling contortions caused by the application of my own fingers to the
focusing screw. The best of all stands is a solid iron pillar firmly
fastened into a brick or stone pier, sunk at least four feet in the
ground, and surmounted by a well-made equatorial bearing whose polar
axis has been carefully placed in the meridian. It can be readily
protected from the weather by means of a wooden hood or a rubber sheet,
while the tube of the telescope may be kept indoors, being carried out
and placed on its bearing only when observations are to be made. With
such a mounting you can laugh at the observatories with their cumbersome
domes, for the best of all observatories is the open air. But if you
dislike the labor of carrying and adjusting the tube every time it is
used, and are both fond of and able to procure luxuries, then, after
all, perhaps, you had better have the observatory, dome, draughts and
all.

The next best thing in the way of a mounting is a portable tripod stand.
This may be furnished either with an equatorial bearing for the
telescope, or an altazimuth arrangement which permits both up-and-down
and horizontal motions. The latter is cheaper than the equatorial and
proportionately inferior in usefulness and convenience. The essential
principle of the equatorial bearing is motion about two axes placed at
right angles to one another. When the polar axis is in the meridian, and
inclined at an angle equal to the latitude of the place, the telescope
can be moved about the two axes in such a way as to point to any quarter
of the sky, and the motion of a star, arising from the earthy rotation,
can be followed hour after hour without disturbing the instrument. Wh