Courier Democrat. (Langdon, N.D.) 1891-1920, 1894-02-22
SCIENCE AMI INDUSTRY.
THE TELsGRAPHING or SHADED
PICTURES.

AoA OA$shS'6gls!gl Z,
One Of the l.ntcst SugHesAiOns-Util-
ising Property Of seIeniun-Mn-
chimes for Business-The Paving Of
the. Future-A Forest Plague.
BY means of Gray's "telautograph,'
described last spring, it Is possible,to
transmit over Il wire for several hun
drcd miles Il diagram or outline draw
ing. With that apparatus the pen of
the receiving instrument is made to Inn
itatc precisely the motions of a stylus
in the sendcr's hand. But the problem
of transmitting in u practically instan-
taneOus way Il shaded picture, like q
photograph, so that an observer can
take it all in ut glance, If projected
upon screen, or SO that a sensitive
plate will register it for further re-
production, is still unsolved.
The principle involved in such an
undertaking is the conversion of large
number OF points in the original design
into electric pulsations and the recon-
ASAOA ouu uopSA uloIiioueLon " NAA>'S
impulses by the receiver. In q recent
issue of the Electrical World H. G.
johnson raises the question whether it
would be better to employ a separate
wire for each pulsation lin a single
operation), and hence to have a bunch
/: Of several thousand wires extending
from one instrument to the other,
OF to send all the pulsations success
siyely over one wire, but sufficiently
close together to make them appear
simultaneous, and thus yield an ap-
parently complete picture to the eye.
Other persons have contemplated using
the former plan; but Mr.. johnson de-
scribes a possible application of the
latter one. He has not tried the expert
ment, and puts the idea forward with
modesty, yet very understandingly.
10 begin with, he would project his
picture with a strong light through a
lens upon small ground glass screen
in front of the transnlitter. The most
important element in the construction
of the latter would be a selenium cell.
Selenium is substance whose electric
in light falling upon it. If piece
of selenium be placed in an electric
circuit, therefore, the insanity Of the
current will vary with that of any
luminous rays falling upon 1t. And
if each minute portion of a transparent
picture, lighted from behind, be ex-
posed separately through an aperture
to selenium cell, the graduations in
electrical intensity will correspond to
the lights and shades of the illustra-
ton. In making such exposures, by the
way, it would be desirable to have
each one alternate with q complete
shutting off of all light from the selen
ium, so that the current would be
broke up into series Of pulsations,
varying, of course, in strength very
delicately. Now, Mr.. Johnson's idea
is that such a cell might be suitably
mounted in a cylinder whose sides
were perforated. There should be a
casing just outside of the cylinder,
with a horizontal slit extending the
width Of the picture on the ground
glass. Owing to their diagonal ar
rangement, only one Of the holes would
I've opposite the slit at time; but only
a small part of a single revolution
would be required to present to the
slit all those in one row. If the frame
holding this cylinder had a slow and
properly regulated downward motion
the first row of holes could be made to
record in a straight horizontal line
the intensities Of light and shade across
the top Of the picture; and the next
row Of holes would register another
series of points along a straight line
q little lower down; and SO on, to the
bottom Of the picture.
At the receiving end of the line
there should be a cylinder similarly
perforated, and rotated at precisely
the same rate Of speed. It should
contain light that would CLEAN
through the holes on to the receiving
screen, but only one hole at Il time
would let light through, and that hole
would correspond in position exactly
to the one in the transmitter which
to the picture Finally, within the re-
ceiving cylinder there should be some
means of varying the brilliancy Of
the illumination according to the inten-
sity of the electric pulsation. The rela-
tive brightness of each point in the
original would then be faithfully re.
produced in the copy. Every child
knows that the glowing end of a stick
which has been thrust in the fire may
be whfrled rapidly enough to make a
ring Of light Impressions from differ
ent points in the orbit come to the eye
in such close succession that they can
not be separated by our perceptions,
and one seems to see continuous
spark. Mr.. Johnson would have his
dots of light projected upon the screen
with such rapidity as to secure SINH
larly simultaneous effect. While this
gentleman frankly says that there are
some difficulties yet to be overcome,
his suggestions are not only interesting
but valuable.
Salenium is unequally affected by
light of different colors. 1t would be
necessary. therefore, in any such APP
paratus to use monochromatic light and
a picture in shades Of only one hue.
However. three such lantern slides as
Mr.. Gray used in the symptom of
color photography recently described in
the Tribune could be reproduced by
Mr.. Johnson's method and then united
in a composite. with the assistance Of
color screens. and thus pictures in col
/ nrS could he telc1I1nhed to any dis