Richmond dispatch. [volume] (Richmond, Va.) 1884-1903, 1894-09-11

photographlng ncbulae. His first photo
graph OF the orion nebnla was secured In
1883. the year following the death 81
Professor Draper. whose incompleted
work he may be said In a manner to have
continued.
This was the state OF Astronomical
photography at the beginning OF 1885,
ten years ago. The value OF photography
for certain kinds OF astronomical work
had been fully demonstrated, and several
cxperimenters-those named and others
were attempting 10 extend still farther
It's usefulness. Professor T.. G.. Picker
Ing, at the Harvard College observa-
tory. was Just beginning those expert.
ments In phOtographing star-spectra,
which resulted in the method now en-
ployed In the execution of that great
compendium OF star-spectra known as
the Henry Draper Memorial" DIR. GIL.
at the Cape Of Good Hope, had al
ready conceived the practlcability OF using
Photography in the work OF chart
making. and was experimenting with
that end IN view. The air-the astronomi-
cal air-was full OF photography, and a
striking advance step at any moment
could be no surprise. 1t came In a de-
cisiYc shape. and was of such a cha
'''N'N4 ~ nv why W OiNhHt 'AANhAHiHsiiii
among astronomers, but also to draw the
attention OF the public generally TO r
subject which had thus far attracted
little notice.
AN HISTORIC INSTRUMENT.
The brothers, Paul and Prosper Henri.
were engaged at the Paris Observatory
IN completing a chart of the ecliptic re-
gion OF the heavens--the region along the
suns path which had been begun in
lsJ2 by NJ. ChacOrnac and work upon
which had been Interrupted by his death
The chart was designed TO aid in the
search for asteroids. II was TO consist
Of seventy-two plates. each about twelve
inches square. and 1t was 10 contain all
the stars down TO the thirteenth magni-
tudc. NJ. Chacornac had completed thir.
ty-slx plates. containing about $4,000
stars. and the Henri brothers. in the
course OF some eight years, had added
sixteen plates. containing 5000 stars,
when they came across an obstacle
which might well stagger the most pa
tent Chart-makcr. They had reached
that part of the heavens where the
oclptic crosses the Milky Way. 1t was
estimated that sore OF the plates repre-
scnting this region would contain from
L.. go to 1900 stars Each square inch
of the plates would contain on an ave-
rage more than 100 stars. To chart them
without omissions. giving TO each star
It's proper place and correct magnitude
might well seem a hopeless task. In
this strait the Henri brothers bethought
themselves OF photography. Expert
ments made with a small telescope spc-
cially adapted for the purpose were so
that work was at once be-
gun on n larger instrument. which was
ready for trial in the early part of 1885.
This instrument has become historical.
Il Is the prototype Of the instruments
which are now used in the great work of
the entire heavens. and a
description Of IL. given at the time by
Admiral MOuchcZ, the director OF the OBJ
iervatory. cannot be without interest
1T consists of two telescopes placed
side by side. enclosed in a four-sided metal
ube. and separated by thin partition,
.unning the whole length Of the tube one
# the detectives. of ten inches I'm aper-
ure. and twelve feet in focal length, is
designed for eyc-obserVatiOn and serves
Is a pointer; the other. of thirteen and
,ue-half inches in aperture, and eleven
Get in focal length. Is corrected for the
'hemical rays Of the spectrum. and serves
or Photography. The optical axis Of
Nese two telescopes being parallel, every
tar kept in the center OF the field of the
.ye-pcce OF the first produces its impress
,ion at the centre of the sensitive-plate
IF the Photographic apparatus. The in
'trumcnt is mounted equatorially. in what
S known as the English style" 1t is pro-
.idcl with the usual driving-clock; but,
as may be gathered from the above-given
description, during the exposure OF the
plate an observer is stationed at the point
r. ready 10 correct any slight error Of
he clock. ana thus keep the instrument
accurately directed TO the stars 10 be
1t may be added that the
,ptcal parts Of this instrument were
made by the Henri brothers themselves.
who are said to he among the most ex-
,crt makers OF telescope objectives in
France.
The work done with this monster
'amera surpassed the most sanguine ex-
ieCtation. An exposure of the sensitive
plate for fifteen minutes proved sufficient
Tor taking the impression of stars down
10 the fourteenth magnitude. With an
exposure of an hour and a quarter stars
we're shown which were estimated to be
II the sixteenth magnitude, and were,
therefore, quite beyond the reach OF an
ordinary telescope Of the same size. The
treat gain in what Sir William IIerschel
allied space penetrating-power thus
'ealized by photography may be illustrated
" the case of the Pleiades. This WELL
Known cluster consists or six or seven
stars, visible to the naked eye. The Old
on astronomy told us that
more than sixty stars" were revealed by
telescope of moderate size" The photo
,raphs taken by Mr.. Rutherfurd showed
bout seventy-five. the falntest being OF
ba 81 n reanpftnHp In 1STQ Mr. lpp1nnn
With his three-foot reflector took photo
.raphs of this cluster, with an exposure
f one and a half minutes. showing "all
n nearly all. OF the stars given in the
maps" a hcliograph-chart of the Pleiades,
nlarged from a Photograph taken by the
Henri brothers, and covering n region
WO degrees in length by one and a half
n breadth contains about 200 stars, of
which fully 200 lie within the space en-
losed by lines connecting the seven
Iaked-eyc stars of the cluster. The plate
howod a number Of faint nebulae. one OF
which had never been seen until II made
Is appearance on this photograph. The
tars are represented by minute discs of
elative sizes, nearly proportional to their
nagniiudes. and defined with neatness
Which could hardly be surpassed I'm a steel
ngraVing To have made a chart of equal
Of the old method of micromet- |
ical measurements, would have eXacted |
he unremitted labor Of several months
ct the original of this chart was secured /
n one hour and twenty minutes. and all !
nat was required of the astronomer was |
o keep the instrument accurately pointed !
0 the stars during this time.
PHOTOGRAPHING 100000 STARS.
The project of making a Photographic |
hart OF the entire heavens already al /,
aided to, was the immediate outcome |
this success Of the Paris astronomers. |
he work was decided 10 be feasible, and |
IS preliminary details were arranged at |
congress of astronomers held at Paris |
4 1851 Various difficulties have been |
ncountered in the prosecution of the |
-ork. as was 10 have been expected, and |
has been thought wise TO proceed |
lowly; but the work is now in progress. !
nd there can be no doubt that within |
sw years astronomers Will be IN the pos
ess.On of a celestial chart OF a fullness |
nj accuracy which IL would be impossi-
le to secure in any other way. The
'ork has been apportioned among /
ighteen ObserVatorics. ten In the North
rn and eight in the Southern Hemisphere.
he plan Is TO make two series Of plates.
he first, embracing stars to the eleventh
Magnitude, is taken with a short ex-
osure, In order to preserve the images
T the stars as distinct as possible This
cries will serve as the basis OF star
analogue. and will contain about a mill
on and a half OF stars. The second,
btained with an exposure OF hfteen