The times. [volume] (Washington [D.C.]) 1897-1901, 1898-08-29
GREAT TELESCOPES.
Sites of More Consequence Now
Than Power of INSTRUMENTS


In the Forum for August The Future
| of Great Telescopes" is discussed by 7.
| ]. ]. See, of the Lowell Observatory, Arl-
| zona who reaches the conclusion that the
! progress of the future is not to 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 frst-class instruments oc-
| cupy high elevations in dry climates. 1T
| is a pity" says the author. Ito have a
| large telescope like that of the Naval OBJ
| servatory at Washington located in such
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 az
Arequipa, Peru, some 5000 feet above the
sea- in climate which is nearly always
clear and dry, has demonstrated the value
of a proper location. 1t is found shat the
definition is at least 100 per cent better
than at Cambridge. Mass. Objects can
be distinctly sen and measured at Are
auipa which were invisible with the same
telescope at Harvard. Where the atmos-
phere is not homogeneous-where one part
is moister or colder than anothe~-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 a distant star passing through this
mass of currents experiences many irreg-
ular refractions. 1t does not fall uniform
ly on the lens 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 danoing' The image, in short.
is blurred and this blurring is worse with
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 1Si5, 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 it is turned into
different positions. and moreover, it tar
nishes in a moist climate. The lenses
made by Clark, of this country. from
French glass are preferable to mirrors
even when the latter are made Of sill
vered glass, and the best telescopes at
present are the refractors. The Yerkes,
In Wisconsin, with a 4a-inch lens, is the