Man's physical universe

xanabras

TELESCOPES 65

has two functions, (1) resolving-power, and (2) light-gathering power.

Resolving-power refers to the ability to produce an image showing

very fine detail.

Increasing the size of the objective increases the lightgathering

power of a telescope just as the dilating of the pupil of the

eye enables one to see better in poor light. Telescopes enable us to see

very distant stars because they gather in so much light from the stars

rather than because they magnify the images of the stars. This is the

fundamental difference between microscopes and telescopes.

Sir Isaac Newton (1642-1727) constructed the first reflector type

of telescope in the attempt to avoid the difficulties

presented by the

refracting lens.

The first giant reflector, equipped with a 72-inch mirror, was constructed

by Lord Rosse, in Ireland, in 1845. A crude, unwieldy affair,

it had none of the automatic mechanisms of modern telescopes. It

had to be twisted about by hand and was kept focused on the object

in the same way.

The mechanism of modern telescopes enables them to be kept focused

on an object in any predetermined position in the sky with great

precision, by means of mechanisms regulated by clocks that move the

position of the telescope at the same rate that the earth turns so as to

keep the object in view.

The astronomer of today merely presses buttons which set electric

motors into action to move the telescope, revolve the dome, and raise

or lower the floor surrounding but independent of the telescope and

even the platform on which the observer reclines.

The Mount Wilson 100-inch Reflecting Telescope Is One of Man's

Most Expensive Scientific Instruments.

The largest telescope in existence in 1936 was the Mount Wilson

100-inch reflector, which has a light-gathering power of 160,000 times

that of the human eye. The four and a-half ton, 13-inch-thick mirror

for this telescope was cast in France and required four years for the

polishing of its surface. As the telescope and its mountings weigh over

a hundred tons, it was a real undertaking to transport all of the parts

up to the top of Mount Wilson, 5000 feet above Pasadena, California.

The revolving dome of the main observatory is over 100 feet high.

The telescope itself is mounted on large hollow cylinders floating in a

huge bath of mercury.

Modem Telescopes Have Extended Man's Knowledge of the Universe.

With modern telescopes man has been able to bring into visible or

photographic view nearly thirty billion stars, or ten million stars for

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