Pittsburg dispatch. [volume] (Pittsburg [Pa.]) 1880-1923, 1889-04-21

though but little used on account OF the
small working force at the observatory. Inc
telescope is provided with circles and
driving clock to enable it to follow the mo-
ton of star. 1t is unfortunate that the in
stitution does not receive the support neces-
sary to keep force to make use of the ex-
eellent equipment it possesses.
In the "dark room" $50 called because all
outside illumination may be excluded from
it) is great deal of apparatus which is en-
tirely unique, and used for the special re-
searches Prof. Langley and his assistants
have been engaged in for long time. The
is famous all over the scientific world is an
investigation of the moons heat. This
problem had almost baffied Investigators
for long time. Poets have always sung
about "the cold moon," and though she GER
tainly sent us light, it was verv difficult to
get indications of heat Large burning
mirrors and lenses were employed to con-
centrate the heat, and delicate Thermometers
were used, but only very small indications
of heat were gotten until Prof. Langley
turned his attention to the problem. Find
ing that the glass lenses used TO concentrate
the moons radiation absorbed a very large
part of the heat, he introduced rock-salt
lenses and prisms into the apparatus. Rock
Sd1I is very uluCu1I W SeL III 1dISO AOAAAN-
geneous pieces, and is very inconvenient to
handle, but it was the only substance suit
able, and so had to be used. y
THE BoLoMETER.
Next it was necessary to geat more del
icate apparatus for measuring slight
changes of temperature, so Prof. Langley
invented the "bolometer," or cheat meas
urer," very small and simple instrument,
which has nevertheless accomplished won
ders. It consists of tube, at the back Of
which are great number of strips of plat
inum wire, through which a current of cleo
tricity is make to travel. 1t is a law that
if the temperature of an electric conductor
is raised, its resistance to the passage of the
current is increased, and so for every vari-
alton in the temperature of the platinum
strips, on which the moons radiation is al
lowed to fall, there is corresponding vari-
alton in the strength of the electric current,
and it then only remains to measure the
strength of the current. This is accom-
plished by very delicate instrument called
the galvanometer, the instrument used here
for these measures being one Of the best in
the world. The whole apparatus is so deli
cate that persons hand, held at some dis
tance from the bolometer, will give large
indication of heat. Investigations of this
sort upon the moon, and, for comparison,
upon terrestrial bodies, such as vessels filled
with warm water, ice, etc., have been made
for several years past, and the results are to
be published in full in the fourth volume OF
the publications of the United States Acad-
emy of Sciences. The practical good to be
derived from these studies is abetter knowk
edge of the laws of radiation and absorption
by our atmosphere and are of great import
ance to the science of meteorology.
LIGHT AND COLOR.
Last year an elaborate investigation was
made of the relative illuminating and heat
ing effects of light of different colors, and
the results published in pamphlet form. In
vestigations were also made as to the time it
took for an observer to notice the appear
ance of faint light and indicate the fact
by pressing an electric key. For very faint
light the time required was half second,
and for q moderately bright light about a
quarter of second.
The library of the observatory occupies
parts of several rooms, and is constantly
growing by the addition of current publica-
tions. Complete files, extending over many
years, are kept of the publications of OBJ
servatories and of scientific magazines, and
are very valuable.
The observatory stands in field of about
ten acres, part of which will soon be used
for the new buildings of the Western uni
versity, and the scientific sanctity of the
place will some day be disturbed by the
baseball and other sports Of the students of
that worthy institution of learning, but 1t is
to be hoped that it will bear the innovation
with philosophic resignation, and will not
have its sphere of usefulness in any way di-
minished.S E. Y. L.