The Seattle post-intelligencer. [volume] (Seattle, Wash. Terr. [Wash.]) 1888-1914, 1892-09-04
CLEAR AIR OF PERU.
The Advantages 1t Offers for
Astronomical Observation.
HARVARD STATION At AREQUlPA.

Professor Pickering Explains why the
South American Mountains Afford
the Best View of the stars.
To the unaided eye the stars present
about the same appearance night after
night, saving that at some times the sky
appears more transparent than at others.
and accordingly we are able to distinguish
somewhat fainter stars. So. too. it APP
peared to astronomers for the first century
after the telescope was invented. But as
time went on and better and better instru-
ments were constructed, it was found that
upon some nights which appeared particu-
larly clear the seeing" was particularly
bad.
To understand what this word "seeing"
means let the reader look at any small
object upon the further side OF a hot stove.
He will notice that its outlines seem to
waver and move about. This is due to the
currents of heated air rising from the
stove. When we look at a bright star
through moderate-sized telescope, We
nearly always observe this same effect. for
the instrument which magniiies the star
magnifies the motion caused by the air
currents in the same proportion. The
astronomers of the last century noticed
the difference in night, but it is only dur
ing the last fifty years that this difficulty
has been felt with its full force.
Astronomers attempt to measure the
position of the stars with one-tenth of a
second of arc. To understand what this
means. We may say that it is equivalent to
measuring the apparent position of an
electric light thirtysfive miles distant
within one inch. Now, if while we are
endeavoring to measure its position some
one takes hold of the lamp and swings it
about his head, We shall find it rather diff
cult to determine its average position with
the required accuracy. That is the copdi-
ton of the astronomer on a night when
the seeing is bad. The remark was once
made, l think, by Mr.. Rutherford, of New
York, noted for his beautiful photographs
of the moon, that during twelve years of
observation he had found only one night
upon which the seeing was really good.
There are two objects in building large
telescopes; one is to gather more light,
and thus enable us to see fainter stars, and
the other is to enable US to see smaller OBJ
jects. But, if the object is constantly
dancing about all over the field of view,
we can see very little more of it with
large telescope than with q smaller one,
excepting that it will appear brighter.
This difficulty has been felt SO keenly
by some astronomers that they have ques-
toned If it was really worth while to build
any more telescopes much larger than
twelve or fifteen inches in diameter, and if
after all there was much that could be
seen from one Of this size. In short, did
not our own atmosphere fix this as the
size beyond which the slight definition
was more than counterbalanced by the ex-
pense and inconvenience of management.
This difficulty was appreciated by the late
James Lick, who specified that his great
telescope should be placed upon noun
tain summit. and he himself selected the
site, hoping by this means to overcome
the irregularities of seeing produced by
our atmosphere. In this attempt we now
know that he was at least partially sue
cessful, and that during the dry season in
California the seeing at the Lick observa-
tory is superior to that at most of the OBJ
servatories placed near the sea level.
Another man, though with less means,
who also appreciated this fact, was the
late Uriah A. Boyden. He left sum of
money to establish, or aid in the establish
ment of, an observatory ''at such an eleva-
ton as to be free. so far as practicable.
from the impediments to accurate obser-
vations which occur in the observatories
now existing, owing to atmospheric intlu-
ences." In the spring OF 1887, this money,
which at that time amounted to nearly
quarter of a million, was entrusted to the
president and fellows of Harvard college,
the income to be expended in such man.
oil of hvyf Il
rector of the observatory.
Besides the primary qualification of
good seeing, or 'steadiness" of the air,
there are four others which it was desira-
BILE to secure if possible. These are trans
parency, freedom from cloud, uniformity
from night to night, and freedom from
dew. If the latter deposits upon the lens
Of the telescope all work, upon even the
clearest nights, must be suspended, exactly
as if the night were cloudy. To avoid this
occurrence various devices have been
adopted, but none are successful upon q
really bad night.
Bearing these points in mind, an expedi-
ton was undertaken the following sum-
mer, to the mountains of Colorado, by the
newly founded Boyden department of
Harvard college observatory. Three loca-
tions were visited, namely: Colorado
springs, altitude 5,035 feet; Seven Lakes
hotel, altitude 10 964 feet, and Pixies Peak.
1873 leS%. u tWcltt-iuCu tcie-
scope was carried TO each of these points,
and numerous carefully made observa-
tions were secured. Pixies Peak Is prob
ably the greatest altitude at which so large
an instrument has ever been employed.
The atmosphere of Colorado was very
transparent, bnt the important quality of
steadiness was found to be lacking.
The next expedition sent out by the
Boyden department was in the winter of
1sSS-S9. Photographic observations were
secured with a tnirteen-inch telescope
from the summit of Wilson's peak, in
Southern California, at an altitude of {, 900
feet. The steadiness of the air was found
to be much greater at this point than in
Colorado, and in many respects the sta
ton was all that could be desired. 1t had
some disadvantages. however practical
one being that it was almost impossible to
obtain clear title to the land upon the
mountain, and it was concluded at length
to seek farther.
In the meantime Messrs. 8. T. and NJ.
II. Bailey had been exploring the west
coast of South America. from Callao to
Valparaiso. and had already established a
station on Mount Harvard, near Lima. at
an altitude of 6,600 feet. Good results
were obtained at this station, but for
various reasons il was decided TO make
further investigations before selecting the
final site. Their attention was called to
Areduipa, Peru, among other places, and
their report upon il was SO favorable that
it was decided 10 send the next expedition
to that point.
The present expedition left the United
States in December, 1880, arriving in
E-fE