The Wichita daily eagle. [volume] (Wichita, Kan.) 1890-1906, 1898-03-22
HUNTING FOR ASTEROIDS.

All of the discoveries Of asteroids with
in the last six years have been made by
two astronomers, Professor Max WOLF
of Heidelberg, and NJ Charlois, Of Nice,
by means Of photography. PROFESSOR
Wolf has lately published an exhaustive
account of his method of conducting the
search. His work Is done with portrait
lenses of five and six inches aperture,
with foci of twenty-five and thirty
inches respectively. The lens is kept &C
curately pointed for exposures OF one and
a half, or. better, two hours. The stars
appear as dots on the plate, while aster-
oids are distinguished by their short
trails, the reason being that during the
time of exposure an asteroid, being
planetary body. will move a short dis
lance in its orbit.
To draw safe conclusions from such OBJ
servations the plates must be duplicate.
They are not exposed simultaneously,
however, but the time of no exposure is
made to overlap that 6 the other. Thus.
plate A is exposed for one hour, and
then begins the exposure of plate B. At
the end of the second hour the exposure
of plate A is closed, while that of plate
p is continued for another hour Part of
the space occupied by the trail Of an as
teroid on plate A will be vacant on plate
B, and vice versa.
For asteroids brighter than the twelfth
magnitude Professor Wolf finds that a
field of some seventy-ive square degrees
may be photographed at one time, under
favorable conditions. that is, an area
about one and half times the size of the
bowl of the great dipper.
When the plates have been developed
they are laid one above the other, with
both films downward, and ar then ex-
amined with a hand-glass. The stellar
points on the two plates will match, of
course Astercid trails. if any there are.
will partially match. one-half of a trail
on one plate overlapping one-half of that
on the ether plate, and thus the trails
can be detected Enthusiastically and can
be at once dis inguished from any imper-
lection on either plate.
Professor Volts catch of asteroids by
this drag-net process since 1891 has been
forty-three new ones and a number OF
others which had previously been discov-
ere. but had been lost.
It is interesting to note that the first
use of stellar photography in regular as
Economical work was as an aid in the
construction Of a chart projected at the
Paris observatory for use in the search
OF asteroids The chart ives begun in
1858 by NJ Chacornac, who at the time
Of his death had completed one-half Of il.
having mapped some 5000 stars. The
work vas then assigned 10 the Henri
brothers. who in the course Of eight years
had cha-ted about 30 900 additional stars.
when they came across an obstacle which
might well appal the most patient chart
maker. They had reached the Milky
Way, and Il vas estimated that the
plates of this region would contain on an
average one hundred stars 20 the square
incn. Happily they bethought them
selves Of photography. and it was ont OF
their experiments IN the use Of tele-
scope camera in surrounding this obsta-
Gle that resulted the 13-inch instrument
with which they tookt heir historis pho
tograph OF the Pleiades. and which dem
onstrated that photography was thence
forth 10 be the prime agency in celestial
chaTt-Elaking.
Curiously enough. the success Of steI-
lar Photography rendered valueless for It's
the labor OF so many years had been ex-
pended. q cart being wholly needless in
searching for asteroids by the method :,
successfully employed By Professors Wolf
and Charlois.