hich he effected
after keeping his eyes in darkness for a quarter of an hour. Kitchener,
indeed, goes so far as to recommend (with a _crede experto_) an
_interval of sleep_ in the darkness of the observing-room before
commencing operations. I have never tried the experiment, but I should
expect it to have a bad rather than a good effect on the eyesight, as
one commonly sees the eyes of a person who has been sleeping in his
day-clothes look heavy and bloodshot.

The object or the part of an object to be observed should be brought as
nearly as possible to the centre of the field of view. When there is no
apparatus for keeping the telescope pointed upon an object, the best
plan is so to direct the telescope by means of the finder, that the
object shall be just out of the field of view, and be brought (by the
earth's motion) across the centre of the field. Thus the vibrations
which always follow the adjustment of the tube will have subsided before
the object appears. The object should then be intently watched during
the whole interval of its passage across the field of view.

It is important that the student should recognise the fact that the
highest powers do not necessarily give the best views of celestial
objects. High powers in all cases increase the difficulty of
observation, since they diminish the field of view and the illumination
of the object, increase the motion with which (owing to the earth's
motion) the image moves across the field, and magnify all defects due to
instability of the stand, imperfection of the object-glass, or
undulation of the atmosphere. A good object-glass of three inches
aperture will in very favourable weather bear a power of about 300, when
applied to the observation of close double or multiple stars, but for
all other observations much lower powers should be used. Nothing but
failure and annoyance can follow the attempt to employ the highest
powers on unsuitable objects or in unfavourable weather.

The greatest care should be taken in focussing the telescope. When high
powers are used this is a matter of some delicacy. It would be well if
the eye-pieces intended for a telescope were so constructed that when
the telescope is focussed for one, this might be replaced by any other
without necessitating any use of the focussing rack-work. This could be
readily effected by suitably placing the shoulder which limits the
insertion of the eye-piece.

It will be found that, even in the worst we