270 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1907. 
of the Andromeda Nebula. You see how little it shows, since a long- 
focus telescope, unless of very great aperture, is not well adapted for 
the photography of faint nebule. When we compare this picture 
with the next one, made by Professor Ritchey with the 2-foot re- 
flector (of 8 feet focal length), we appreciate immediately that the 
40-inch, in spite of its great advantages for certain classes of work, 
is wholly unadapted for other investigations. As you know, a re- 
fractor of much smaller aperture and of shorter focal length would 
also give a photograph of the Andromeda Nebula far superior to 
anything that could be taken with the 40-inch. 
If we look at the next slide, which shows Professor Barnard’s 
10-inch Bruce telescope when it was mounted on Mount Wilson, 
where he was using it to photograph the Milky Way, you will see an 
instrument that is very small and inexpensive as compared with the 
Yerkes telescope. It has a 10-inch Brashear lens of 50 inches focal 
length and certain smaller cameras attached to the side of the tube. 
With such an instrument as this, superb photographs of the Milky 
Way, like the one illustrated in the next slide, can be taken, which are 
indispensable for investigations on the distribution of stars in this 
part of the heavens. Excellent work can also be done with a much 
smaller lens, provided with a very simple mounting.“ A fine instance 
of systematic work with a portrait lens is afforded by Mr. Franklin- 
Adams’s photographic map of the northern and southern heavens. 
Tt is hardly necessary to recall the fact that the 40-inch could not 
do this work at all. If we attempted to photograph the Milky Way 
with it, we might get a very small region on a very great scale, but to 
give us any notion as to the general distribution of stars in the Milky 
Way the 40-inch would be a total failure. However, if it were a 
question of studying some star cluster like the one shown in this 
slide, which would occupy a very small region indeed of the Milky 
Way, the.40-inch would enable us to pick out the separate stars, to 
study their individual phenomena, their changes in light and position, 
while such work could not be done on photographs taken with a por- 
trait lens. 
I have shown these miscellaneous illustrations for the purpose 
of emphasizing, what is perfectly well known to all of you, that 
each instrument has its particular fields of work, in which it can 
accomplish, or permit to be accomplished, various investigations 
which are not within the reach of other kinds of telescopes. But 
I now wish to discuss the question somewhat more specifically, 
“Professor Barnard has illustrated in the Astrophysical Journal some of the 
admirable results he has himself obtained with a cheap ‘‘ lantern lens ”’ belong- 
ing to an ordinary stereopticon. A photograph obtained by him with this lens 
is reproduced in plate I. 
