Evening star. [volume] (Washington, D.C.) 1854-1972, 1903-11-14

"oulu DuTH q more INTO the him OF the IdSI-
est Photographic plate known. in the least
possible fraction of a second for operating
camera shutter. By leaving the silver OF
the surface of the reflector, the luminosity
of the sun is reduced to one-twentieth OF
what 1t would be were the looking glass
surface allowed to remain
The box of the big camera is divided into
several rooms, the box proper being an am
pie dark ROOM such as photographers EN-
ploy to develop ordinary photographs. In
the north wall of this apartment is win
dow opening into the long shed which we
call the bellows and covered by big,
camera shutter, behind which stands
skeleton plate-holder mounted upon a ped
estal of iron, which itself rests upon pier
of masonry extending into the earth The
lens outside being stationed upon one pier
and the Photographic plate in the holder
resting upon another, jars and vibrations
of men moving near are thus avoided. The
dark room being tightly closed, the sensi-
tive plate being put in the holder with its
face toward the shutter, and the image of
the sun being projected by the mirror
through the shingled camera bellows ana
against the closed shutter. all that now re-
mains to be done is to open the shutter
and allows the image to impinge upon the
plate.
Taking the Picture.
1 was now to witness the actual photo
graphing of the suns image. this explana-
ton of the apparatus having first beer
given to me in the technical lingo which
astronomers employ. At IL 80 I'M, stand
ard time, DIR. G. F. Culon, an assistant, I'M
covered the lens and mirror, while Mr..
Peters stationed himself in the dark room
and adjusted the plate in its holder. By
dnt of careful turning at a wheel the as
sistant caught the sun with the mirror and
reflected it through the lens so that its
image exactly covered black bull s-eye on
a target painted upon the outside of the
shutter. This target l could see by glanc-
ing through the dark chamber inside the
shed. DIR. Culon then produced from his
pocket dark red glass in a metal frame.
through which he squinted at the sun to as
himself that no small riffs of cloud
might be trespassing in the path of vision
Satisfying himself on this point, he called
through a speaking tube the reading of a
thermometer which hung near the lens.
'.Sixty-niner said he. "All rightr' came
Mr.. Peters voice through the tube. This |
observation was essential to the sharpness
of the picture, inasmuch changes of tenn
perature alter the volume of the lens and
mirror and change the focal length of the |
former. Mr.. Peters was holding in his hand
a screw which moved the plateholder either !
farther from or nearer to the lens To adapt |
it's distance to the thermometer reading |
was a matter of great care, although not of |
very vigorous turning at the screw. Be |
tween the coolest day in winter and the |
hottest in summer the focal length of the |
lens is altered nearly an inch.
'AIl rght?" came the voice from the little |
house.
IAN rightw answered the voice of the as
sistant.
"Snap!r replied the shutter.
And Old Soils portrait was taken.
The Spots Discovered.
Ten minutes later the specialist emerged
from the dark room holding up against the
window-lght a glass plate Xxi inches
square, transparent at the borders and with !
A i'm ia |
in the center In the upper half of the big
black spot were several transparent
bIotches, ragged at the edges.
ssWell, I got them all right" said Mr..
Peters, with smile of satisfaction.
"Got what?" asked.
Sur spots" said he.
When the plate was dried he cut the date
of the exposure into the transparent edge
with a diamond, and filed it away in a
pigeonhole. In the same case reposed $50
such plates, all nled away with their dla-
records.
This solar photography, begun in Janu-
ary 1898, had been quietly carried on at |
the naval observatory until a few weeks
ago, when the vanguard of the sun spot
which has since excited the
scientific world, made its first register upon
Mr. Peters negatives. 1t was he who first
on this side of the water the
approach of these great blotches the
suns surface. The naval observatory is !
the only institution in the new world which
keeps a Photographic diary of the suns
doings. Its Observation-Disclosures such is
the scientific name of the great camera
deseribed-is the only instrument of the
Kind now being daily used in America.
Measuring the Spots
To measure these great spots each day is.
of course, a simple matter. 1t being known
ubat fraction of the suns great diameter |
is represented by the diameter of it's small
image, scale applied under
a microscope to any mottled negative will
anproximate the dimensions of the spots
if a simple formula be applied The largest
SPOT yet photographed by the photo-helio-
graph was conspicuous on October s. 1t
was about 900 miles long by about 3d.
600 miles wide. A great cross formed by
twenty-one earths. side by side horizontally
and seven earths, one on top of the other,
vertically, could enter this great spot pre-
Stunning it to be a cavity. But are sun
spots vast cavities, as many astronomers
opine?
This great spot, photographed on Oc-
tober 8, and then seen on the solar limb, or
edge appears on the negative to be pro-
lection rather than a depression" said