200-INCH HALE TELESCOPE—HUBBLE ZAC 
low-expansion glasses have been developed, methods of parabolizing 
have been perfected, and engineering problems of constructing 
telescopes have been solved as they arose. 
The 40-inch refractor was installed at Yerkes under the direction 
of George E. Hale. He clearly saw that, regardless of the success 
of this telescope, the quest for still greater light-gathering power 
depended upon mirrors rather than lenses. Refractors were pref- 
erable for certain types of work (including, for instance, visual 
resolution of double stars, precise measurement of position, wide- 
angle photography, ectc.), but for light-gathering power, with all that 
it implies, the future lay with the reflector. Because the reflections 
are from the front surfaces, transparency and absolute homogeneity 
of the glass are not demanded; the mirror may be supported from the 
back and sides, instead of from the rims alone as in the case of lenses, 
and, of course, there are no color effects. 
Hale took the lead in America in encouraging the development of 
large reflectors. A 24-inch of unusual perfection was made by G. W. 
Ritchey and installed at Yerkes. It proved so successful that plans 
for a 60-inch were immediately set in motion. When Hale left 
Yerkes to establish the Mount Wilson Observatory, he was able to 
transfer Ritchey and the unfinished 60-inch mirror to Pasadena, where 
the telescope was completed in 1908. The work of the 60-inch on 
Mount Wilson so fully justified the faith in larger reflectors that plans 
for a new one were immediately made, this time for a 100-inch mirror. 
This reflector, completed during the first World War, marked an 
important epoch in the history of astronomy. It is still the greatest 
telescope in operation. Four large reflectors with mirrors from 60 
to 84 inches have since been completed (two in Canada and two in the 
United States), and others, including a 120-inch for Lick Observatory, 
are in process of planning or construction. 
The 100-inch opened up new fields of investigation of the very first 
importance, and furnished glimpses of even richer fields beyond. If 
more light-gathering power were available, these more distant fields 
could be explored. In the face of this challenge the possibility of 
larger telescopes was the favorite topic of conversation among astron- 
omers at Mount Wilson, and presumably at other places as well. 
We talked of 200 inches, or 300, and even dreamed of still more light. 
One of the group, F. G. Pease, drew tentative designs for a 300-inch, 
and demonstrated that the engineering features were not impossible. 
Again Hale took the lead. Through his efforts funds were secured 
in 1928 in the form of a gift from the International Education Board 
to the California Institute of Technology for the establishment of an 
astronomical observatory and laboratory. An Observatory Council, 
with Hale as chairman, and with the greatest experts in the country 
as advisers, administered the details of the project. When Hale 
