The times., 1898-08-30
GREAT TELESCOPES.
Sites of More Consequence Now
Than Power of Ihstrume nts.
(From the Baltimore SUM

(From the Baltimore SUM
In the Forum for August The Future
of Great Telescopes is discussed by I.
j. J. See, of the Lowell Observatory, Ari-
zona, who reaches the conclusion that the
progress OF the future is not 10 be so
much in the increased size and power of
telescopes as in the selection of suitable
sites The existing telescopes are large
enough-they gather enough light TO give
effective vision-but, on account OF the
bad location of most of them, they do
not give sharp definition. The view they
give of the heavenly bodies is blurred and
unsatisfactory because the atmosphere
through which light reaches them is not
clear. dry or steady. Absolute transpar-
ency is perhaps, unattainable, but prog
ress in astronomical work will be made
in the near future, chiefly at observa-
tories where first-class instruments oc-
cupy high elevations in dry climates. 1T
IS a pity" says the author, Ito have
large telescope like that of the Naval OBJ
seryatoTy at Washington located in such
a climate, because IT can at best show
only objects which are moderately easy,
whereas, If IL were placed in the high and
dry plateaus of the Southwest it would
become one of the foremost telescopes of
the world. In like manner the 40-inch
Yerkes telescope in the cloudy belt OF
Wisconsin must at least be handicapped.
Such a telescope located in the elevated
plains of Peru or in New Mexico might
render great service to the science of the
stars"
The 1s-inch telescope located eight
years ago at Harvard Observatory at
Arequlpa, Peru, some S,000 feet above the
sea in a climate which is nearly always
clear and dry, has demonstrated the value
of a proper location. II Is found shat the
definition" is at least 100 per cent better
than at Cambridge, Mass. Objects can
be distinctly seen and measured at Are
qlipa which were invisible with the same
telescope at Harvard Where the atmos-
phere is not homogeneous-where one part
is moister or colder than anotle--the
passing rays Of light will be bent. The
air will be moving in streams or currents
of differing densities and varying refract-
i've powers, with the result that the light
from distant star passing through this
mass of currents experiences many irreg-
ular refractions. IL does not fall uniform
ly tho Ions of the telescope but in
patches. thus spelling the definition. The
image seen by the observer, instead of
being sharply defined, becomes a con-
fused mass OF points heaped together and
constantly dancing" The image, in short
is blurred. and this blurring is worse with
a large telescope than with a small one
There is, therefore, limit TO the size of
telescopes arising from the unsteadiness
of the atmosphere. Inasmuch. however,
as the density of the atmosphere is halv-
ed with every 81 miles of elevation. this
limit can be extended by placing observa-
tories on high mountains To be added
to the advantage of the steadier and
purer air of great elevations is the fact
that the number of clear nights suitable
for observations is vastly greater in such
situations.
The refracting telescope Mr.. See thinks,
is to be the instrument of the future
Lord Roses 6-foot reflector, completed
in 1S45, gives results much inferior to
those of comparatively small refractors.
Roses great mirror never gave good
definition" Its shape varies, by reason
of its own weight, when 1t is turned into
different positions, and, moreover, il tar
nishes in a moist climate. The lenses
made by Clark, of this country from
French glass are preferable 10 mirrors
even when the latter are made of sill
vered glass and the best telescope. at
present are the refractors. The Yerkes.
in Wisconsin, with a 40-inch lens. is the
largest, but the Washington. 26-inch, the
Lick, 36-inch, are large enough for most
purposes. There are also large and eX-
cellent refracting telescopes at the Uni
Versity of Virginia and at Lowell, Ariz.
The Lick and the Lowell refractors have
the advantage of being well placed, in a
dry climate and lofty situation. The Low
ell telescope, with an aperture of but "a
inches, has disclosed many phenomena
not visible through larger instruments at
inferior locations. For spectroscopic
work, which requires much light, the
large rejecting telescope may be, 1t is
conceded, very useful, even though its
definition be poor All the best telescones
are In the Northern Hemisphere, which
mas already been pretty well worked The !
astronomical desideratum of the present
day according to Mr.. See is a giant tele-
scope located in Peru or northern Chile.
in the Southern Hemisphere where the
fixed stars and nebulae over a large ex-
panse near the South Pole are very little
known.