Have we at length reached the limit
in size? If we include reflectors, no, since we have mirrors of 60
inches aperture at Mt. Wilson and Cambridge, and a still larger one of
100 inches has been undertaken. It is more than doubtful, however,
whether a further increase in size is a great advantage. Much more
depends on other conditions, especially those of climate, the kind of
work to be done and, more than all, the man behind the gun. The case is
not unlike that of a battleship. Would a ship a thousand feet long
always sink one of five hundred feet? It seems as if we had nearly
reached the limit of size of telescopes, and as if we must hope for the
next improvement in some other direction.
The second great advance in astronomy originated in America, and was in
an entirely different direction, the application of photography to the
study of the stars. The first photographic image of a star was obtained
in 1850, by George P. Bond, with the assistance of Mr. J.A. Whipple, at
the Harvard College Observatory. A daguerreotype plate was placed at the
focus of the 15-inch equatorial, at that time one of the two largest
refracting telescopes in the world.
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