THE 200-INCH HALE TELESCOPE AND SOME 
PROBLEMS IT MAY SOLVE! 
By Epwin Hussite 
Mount Wilson Observatory 
[With 10 plates] 
In 1609 Galileo turned his telescopes toward the sky. His favor- 
ite—it was the fifth, finished within 6 months of the first trial—was 
about 5 feet long and had a lens about 2 inches in diameter. It 
magnified nearly 30 times and its light-gathering power was equal to 
about 80 human eyes. He called it ‘Old Discoverer,” and with it he 
saw mountains on the moon, phases of Venus, four moons of Jupiter, 
and stars innumerable beyond the limit of the unaided eye. 
It was then that the explorations of space began—the explorations 
that have swept outward in wave after wave as telescopes developed, 
until in our time we study a region of space so vast that it may be a 
fair sample of the universe itself. Today there is nearing completion 
a new telescope, far more powerful than any previously made, and it 
is proper to consider its significance both as an engineering achieve- 
ment, and as an instrument for further explorations. With this end 
in view, I propose to discuss briefly the development of telescopes in 
general, the 200-inch in particular, and some of the problems it may 
help us to solve. 
Galileo’s optic tubes with single-lens objectives grew rapidly into 
telescopes from 20 to 25 feet long with lenses 2 to 3 inches in diameter. 
There the development stopped, for practical purposes, because of 
the engineering difficulties with still longer tubes. 
The longer focal lengths were considered desirable in order to over- 
come color difficulties. With a single lens, each different color was 
brought to a focus at a different distance from the lens. Hence the 
image, when focused for any particular color, was blurred by the out- 
of-focus images in other colors. The long telescopes represented an 
attempt to spread out the images of different colors over so long a 
distance that one color could be focused with minimum interference 
1 Alexander F. Morrison lecture, delivered in Pasadena, Calif., April 8, 1947. Reprinted by permission, 
with slight alterations, from Publications of the Astronomical Society of the Pacific, vol. 59, No. 349, August 
1947. 
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