Spirit of the age. [volume] (Woodstock, Vt.) 1845-1913, 1900-03-17
THE ART OF HELIOCRAPHlNC.
How Messages Are Thus Transmitted IL
South Africa.

NOW MessaSeS are lnuS 1Thusthitteu III
South Africa.
The heliograph system of transmit
ting messages is in use in South
Africa. Briefly speaking, the method
consists in the reflection of flashes OF
light from one mirror to another,
which can be done at long distances,
using the Morse system OF dots and
dashes, as in telegraphy. The field
Photograph equipment OF the signal
corps of the United States consists OF
one sun mirror, one station miro, q
screen, sighting rod, screw driver,
mirror bar and two tripods.
The sun mirror has an unsilverel
spot at lis centre, the station mirror
q paper disk; in o'her respects thev
are similar. The tangent screw at
tachment to the frame affords the
means of revolving the mirror about a
horizontal axis. The support to the
frame has conical projection accur-
ately turned to tit the socket of the
mirror bar and grooved to receive the
clamp spring. The screen is provided
with key, by which. in connection
with the action of the spring, it is
operated to reveal and cut off the
fash. The sighting rod is fitted to
the socket Of the mirror bar and is
clamped in the same manner as the
mirrors. 1t carries at one end Il NOV
able disk, viii h, when turned down.
reveals the front sight. A piece OF
white paper is slipped into the disk
to receive the shadow spot and a
slight puncture made therein coincl.
dent with the point Of the front sight
as a guide in adjustment.
The position of the sun is the guide
for determining whether one or two
mirrors should he used. When the
sun is in front of the operator the sun
mirror only is required. With the
sun in the rear of him both mirrors
should be used, although single
mirror may often be worked to adj
vantage with the sun we'll back Of the
operator. In the former case the rays
of the sun are reflected from the sun
mirror direct to the distant station;
in the latter they are reflected from
the sun mirror to the station mirror,
thence to the distant observer
In the former case, when the ap-
paratus is properly in position, the
mirror is moved by means OF slow
motion screws until the shadow spot
falls upon the disk of the sighting rod.
The fash is then visible to the dis.
tant observer. 1t is always necessary
to keep the ''shadow spot" in the
disk while signaling. The screw is
attached to the tripod and placed in
front OF the signaling disk in order to
intercept the flash.
For signaling with two mirrors the
apparatus is properly adjusted and the
station mirror is turned until the re.
Election OF the distant station is
brought accurately in line with or is
covered by the unsilvered spot and
the reflection of the disk. Then full
flash is thrown from the sun mirror
upon the station mirror so that the
'shadow spot" falls upon the centre
OF the dish. This makes the flash
visible at the distant station.
Signaling is effected by depressing
the screen for periods of time required
to display flashes corresponding to
dots and dashes. The dot is repre-
scented by momentary exposition of
the fash, and the duration of this ex-
position constitutes the "unit OF
time"
The range over which signalling
may be effected by means OF this in
strument, under favorable atmos.
pheric conditions, is limited only by
the convexity of the earth. The square
mirror is adopted in preference to the
round, as containing about one fourth
more reflection surface for practically
the same packing space. Signaling
at moderate range by night may be
effected by moonlight; also by the
employment OF artificial light.