The morning call., 1895-03-03

guiding telescope with which the observer
does his usual work is clamped the photo
graphic telescope. The two correspond in
( every particular save that one is for the
/ eye, the other for the sensitive plate.
AS rapidly, as the photographs for the
map are finished they are marked with the
Gate and location and stored. At Green
wich racks are placed in the library to
/ hold the plates. AS soon as the first series
for the map is fastened in each observatory
second covering the same ground will be
begun. This is done to avoid false stars
and to escape the inconvenience of insensi-
BILE points which might exist on the plates.
The second series will only differ from the
first by the position of the stars-that is, a
star situated in the corner of a plate of the
trst series should be as near as possible
the center of plate of the second series,
SO that a quarter of each of four plates of
the second series will be found on one of
the first series.
The plates made for the catalogue photo
graph the stars to the eleventh magnitude
only. Each of these plates is given three
poses of unequal length in such way that
each star is represented on the same plate
by three images of different intensity and
separated by two to three tenths of milli-
meter. These poses are 5 minutes min
utes, 30 seconds and 20 seconds in length.
For the sake of verifcation two series of
plates are made for the catalogue.
Taking the photographs does not finish
the work. For the map there is the still
puzzling question of putting together the
plates and publishing them. So far the
question has received but limited atten-
ton, other more immediate problems
claiming solutions.
The most serious question at present is
measuring the catalogue plates. Each star
up to the eleventh magnitude on each of
the over 1000 negatives is to be accurately
measured for its right ascension and
declination. AS there will be some
1000 600 of the stars, the immensity of the
task is plain.
The task of measuring the 1000, 900 stars
of the catalogue is evidently going to take
a long time, each observatory having on an
average over 100000 to locate. At the OBJ
servatory of Paris the measuring is well un-
der way The department was established
by the Messrs. Henry and directed by a
young American woman, Miss Klumpke,
an astronomer and mathematician of re-
markable skill and learning. She is as
sisted by woman. AT Greenwich, too,
the astro- Photographic work is mainly done
by two women, Miss Russell, talented
| Girton girl, directing it.
| The catalogue, when completed, will. it
| is computed fill some forty volumes of
1000 pages each-fifty stars to a page.
And when Will it all be done? That is
question at which the astronomers them
selves shake their heads. cat least a
dozen years" they say in Paris at can
not be completed for twenty or thirty
years, probably not for fifty, saws DIR. Gill
Long as it may be, the work has none of
| the hOpelesSness of the old methods of
cataloguing stars and besides its progfess
! brings with it constantly new discoveries
and new contrivances. Under the impulse
of this international effort in stellar pho
! Biography some most astonishing NEGATIVES
have bppn obtained hu
Thus Mr. Gill obtained on one of the map
| plates by exposure of three hours and
! twelve minutes, instead of forty minutes, a
| photograph which contained so vast a
number of stars that it was estimated that
II that length OF pose were allowed for all
the plates of the star map it would contain
! some 100000, 600 stars instead of from 30,-
0O0,C00 to 100000, as estimated now
! In way the observatories are learning
what to do as they do it, and when the
undertaking is completed it is certain that
! II Will have suggested large number of
! future Investigations as well as have given
! to the world a trustworthy map OF the
| heavens for the year of 1900, a map and
catalogue which will be a basis upon
which future ages will be able to estimate
the slow changes, the revolutions by long
periods which are produced by the uni
verse and which before have escaped as
| tTonomers because they lacked sufficient
! data for comparison.
Another and most democratic result is
dwelt upon by the eloquent originator of
the map, the late director of the Obsefya-
tory OF Paris, NJ. Mouchez. ''It is no
longer" says he, ''the great observa-
tories which will have tne monopoly
OF the study of the sky; it is no
longer by the aid of great and costly in
struments SO inconvenient to handle so
rarely useful, that the most interesting dis
coveries. will be made, but it will be by
simple micrometers on plates which will
allow the observer to keep before him in
his workingroom an image of the sky
easier to study, more complete and more
exact than he could have under the best
telescope.
"The population OF these plates and