It is
also necessary to be well acquainted with a number of nebulae
which look very much like comets. The search can be made with
almost any small telescope, if one is careful to use a very low
power. With a four-inch telescope a power not exceeding twenty
should be employed. To search with ease, and in the best manner,
the observer should have what among astronomers is familiarly
known as a "broken-backed telescope." This instrument has the eye-
piece on the end of the axis, where one would never think of
looking for it. By turning the instrument on this axis, it sweeps
from one horizon through the zenith and over to the other horizon
without the observer having to move his head. This is effected by
having a reflector in the central part of the instrument, which
throws the rays of light at right angles through the axis.
[Illustration: THE "BROKEN-BACKED COMET-SEEKER"]
How well this search can be conducted by observers with limited
means at their disposal is shown by the success of several
American observers, among whom Messrs. W. R. Brooks, E. E.
Barnard, and Lewis Swift are well known. The cometary discoveries
of these men afford an excellent illustration of how much can be
done with the smallest means when one sets to work in the right
spirit.
Pages:
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152