The morning call., 1895-03-03

to fact that had been slowly growing into
practical recognition and use for some
years back and it brought to definite organ
ization and beginning an important pro-
iect that astronomers had talked about a
good deal, but had never shown them
selves quite ready to set about, namely, the
making of a great star map by interna-
tional cooperation Bringing into use the
best appliances of photography that
could be devised 1t was proposed to photo
graph the entire heavens, north and south.
But so vast an enterprise, II was conceived,
could be satisfactorily accomplished only
by getting combined on it leading univer-
sites IN different parts of the world.
NJ. MOucheZ, director of the Observatory
OF Paris, where the Henry brothers were
conducting their experiments, proposed
that the French Academy of Science take
the work under Its patronage. The
academy did not hesitate, and in October,
1856, sent invitations to all the leading
foreign observatOries asking them to send
delegates TO an international conference on
the subject. This congress, which gath
cred IN Paris in April, 1887, was composed
OF thirty-six foreign and twenty French
delegates.
In order to understand what this con-
gresS had TO do 1t will be wise, perhaps
to see exactly what is meant by
star-map. Every one is familiar with
as hollow ball, in the center of which
is the earth. Around the earth this hol-
low ball seems to turn once in every
twenUy-fOur hours on an axis which
has its pole at the end of the Little
Bears tail for those of US who are happy
enough to live in the northern hemis-
phere. This hollow ball has a surface
OF some $1,000 square degrees, every point
of which is, under the telescope, packed
with stars, which popularity are called
fixed because when viewed from night
to night even over number of years they
seem never to change place. These points
and groups always appearing in the same
places in the sky have tempted men since
the beginning of the world to survey the
sky in the same way as they did the earth,
fixing the location of each in its relation
TO others and giving all names; that is to
make maps of the sky.
1t seems like a useless task this exact
noting OF the position of fixed stars, this
computing of their celestial latitude and
rarely more intelligent than adding up
columns of figures. The astronomers
however, knew why thew worked at this
tedious business. They had discovered by
comparing the positions given to stars in
different catalogues since Hipparchus that
these fixed bodies really moved. All they
had been able to discover of the slow
march of the sun, of the apex of the solar
way, of local star drifts had been drawn
past. 1t was reason enough to continue
their observations, this hope to give to the
future data for making discoveries similar
to those of the laws OF the movements OF
the stars.
very little imagination will show how
the astronomers proposed to go to work to
make this map. Recall the notion of the
celestial sphere as hollow ball rotating
around the earth as a center; it is evident
that an observer on the earth will see but
one-half of the ball at a time and that the
half he sees will depend upon his position,
on the earth's surface 1t viii be neces-
sary, then, to have observers in different
parts of the earth surface in order that no
part of the heavens will be without the
range of those engaged in photographing
Suppose that we have five observatories
from which all of the southern half of the
celestial sphere is visible, five from which
the northern half can be seen, it will be a
simple matter to divide up the ball into
ten zones and give one to each observatory
Suppose now that each one of the ten
obserVatories takes on an average 1000
photographs When all have finished the
work assigned there will be 10000 photo
graphic plates which, if the skies were
divided up properly to begin with, will in
clude every star to be seen in the universe
up to a certain magnitude. The telescope
for taking these photographs the plates
used, the methods for measuring must pro-
duce in each observatory the same results,
1t IS evident that many nice points of
, detail had to be settled by the congress. 1t
speedily reached, however, sufficient con-
cluslons to enable the members to go home
ana prepare the apparatus necessary to
begin work
Two years later, September, 1889, the
permanent committee of the international
map met again in Paris. Nineteen OBJ
serVatories were heard from. The next
step OF the committee was to divide up the
SKY between the nineteen observatories. 1t