THE OPEN LETTER
It should be a matter of no little pride
to Americans that all the great refracting lenses of the world have
been ground in the United States. The firm that has done most of this
work is that of Alvan Clark
and Sons, of Cambridgeport, Massachusetts. Alvan Clark, the father,
(1808-'87), was the son of a New England farmer, and taught himself
engraving and portrait painting. It was while he was a portrait painter
in Boston that he became interested in the manufacture of telescopes.
In 1844 he constructed a small reflector, the success of which led him
to the grinding of lenses. It was not long before the reputation of the
Clarks, father and son, as lens manufacturers became known the world over.
In this great work the Clarks have won imperishable fame. Alvan Graham
Clark, the son (1832-'97), joined in his father's work at an early age,
and it is under his direction that some of the finest lenses have been
made. Five times between 1860 and 1892 the Clark firm was called upon
to construct "a telescope lens more powerful than any in existence,"
and each demand brought forth a greater glass, ending with the giant
Other large refracting telescopes are the
36-inch at Lick Observatory, Mt. Hamilton, California, the 26-inch at the
U.S. Observatory at Washington, D.C., the 24-inch at Harvard University,
Cambridge, Massachusetts, and the 30-inch at the Alleghany Observatory,
Riverview Park, Pennsylvania. In Europe, the famous lenses are the
30-inch at the Imperial Observatory, near Petrograd, Russia, the 32-inch
at the Nikolaieff Observatory, Russia, the 31-inch at Potsdam, Prussia,
and the 28-inch at the Royal Observatory, Greenwich, England.
* * *
These are the great lenses of the world.
The famous reflectors are much larger. Two of the most remarkable
reflecting telescopes ever put in place are in the observatory on
the summit of Mt. Wilson, near Pasadena, California. One of these
mirrors is made of silver on glass, has a diameter of 60 inches and
weights nearly a ton. The other mirror has a diameter of 100 inches;
the tube that supports the mirror is 43 feet long, and, together with
its mountings, weighs about 20 tons. Besides its giant lens, the Lick
Observatory is equipped with a 36-inch reflector. At Harvard University,
there are two reflectors—60-inch and 28-inch. Next in size is
the 24-inch reflector at Yerkes Observatory. Outside of the United
States there are still more powerful reflectors—the 72-inch at the
Dominican Astronomical Observatory, Victoria, B.C., the reflector of
similar diameter at Biru Castle, Ireland, the 61-inch at the National
Astronomical Observatory, Cordoba, Argentina, the 60-inch at Ealing,
England, the 48-inch reflectors at Melbourne,
Australia, and Paris, France, and the 39-inch at Meudon, France.
ALVAN G. CLARK SEATED BESIDE THE GREAT|
40-INCH YERKES LENS