178 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1949 
dropped out, Max Mason took over the chairmanship. It was decided 
that a 200-inch reflector was as bold a step beyond the 100-inch as 
could be justified in view of the unknown problems, both optical and 
engineering, that might be encountered. Laboratories and shops 
were erected on the California Institute campus, a site for the ob 
servatory was found on Mount Palomar, a disk of pyrex glass was 
achieved by the Corning Glass Company, and the project proceeded 
steadily until it was interrupted by the war. Work was resumed soon 
after VJ-day, and the telescope has since been completed. 
The proper fields for the 200-inch are determined primarily by its 
immense light-gathering power. Because adequate consideration of 
all the possible applications would require more time than is now 
available, I propose to limit the following discussion to three typical 
problems. These problems are, first, the existence of canals on Mars; 
second, the relative abundance of the chemical elements in stars; and, 
third, the large-scale structure of the universe. Each problem 
represents a particular aspect of light-gathering power, namely, 
resolution, dispersion, and depth penetration. 
As a brief introduction, let me comment on the telescope itself. 
The mirror intercepts a beam of light 200 inches or 17% feet in 
diameter—in other words, it gathers as much light as a million human 
eyes, or four 100-inch reflectors. It funnels this light to an image at 
the primary focus, 55% feet in front of the mirror. There an image 
of the sky is formed such as you may see on the ground glass of a 
camera. This image may be examined visually with a microscope, 
recorded on a photographic plate, analyzed with a spectrograph, or 
studied by other techniques. Actually, most of the work will consist 
of direct photography or spectrum analysis. By using long time 
exposures, it is possible to photograph stars or nebulae several times 
fainter than can be seen in the eyepiece. For this reason, the 200- 
inch is best described as a huge camera. 
Now let us consider some typical problems for the 200-inch. I shall 
start with a problem concerning a member of the solar system. The 
telescope will not be turned on the sun because of temperature effects— 
in some ways it would act as a burning glass. Nor does it offer any 
unique advantages for the study of the moon. In that field it will 
serve merely to improve data of a kind that can be got nearly as well 
with several other telescopes. In the field of planetary photography, 
however, the opportunities are unique because, for the first time, it 
may be possible to photograph all that the eye can see with a telescope 
of moderate size. An immediate application is to the highly contro- 
versial question of canals on Mars. 
The canals are described as very fine, dark lines running along great 
circles, sometimes doubled, and often converging or crossing at spots 
called “‘oases.”’ Such fine, hairlike patterns, superposed on the back- 
