New-York tribune. [volume] (New York [N.Y.]) 1866-1924, 1881-05-08
SCIENCE FOR THE PEOPLE.
THE HFLIOGRAPH.

The Photograph, which was prominently
brought into notice III army signalling IN the
recent campaigns in Afghanistan and South
Africa, consists Of a circular mirror, generally
about Alp inches in diameter. mounted on n
small but very firm folding tripod stand. II is
so mounted as TO be capable Of motion both
horizontally and vertically. G., in azimuth
and altitude. The horizontal motion Is inn
parted to 1t by means of a slow motion tangent
screw, working into worm thread cut round
the horizontal plate forming the base OF the
instrument The vertical arrangement, how
ever, is quite different; the mirror Is hung by
a compile of horizontal trunnlons TO pNT OF
brackets rising from the horizontal plate. IN
der the mirror lies a key similar IN appear
ance TO q telegraph signalling key, hinged
at the forward end to the horizontal
plate. and kept upward by fiat spring
beneath A small rod connects the movable
end of this key or lever 10 the upper part of
the back of the mirror, so that when the key
il depressed, the mirror Is tilted upward
through a small angle. This rod Is capable OF
being shortened or heightened by being screwed
through the lump by which it is attached 10
the mirror. This altering the length OF the rod
has the effect of altering the inclination OF the
mirror to the horizontal plane, !. g., OF giving
it motion in altitude. The mirror has small
portion of the silverng removed from It's
exact centre. For directing the flash, NOV
able arm or bracket, twelve OF fifteen inches
long, IS fitted 10 the head of the tripod, and Is
capable of horizontal motion, and can be
slides "a small vertical rod, fitted Of It's upper
end with q small ring caryinga pair OF stout
cross wires.
70 work the instrument, II is set mp facing
toward the point to hc -iruallcd to; tho arm
and TOD carrying the cTc>--Virc7 are now
moved and adjusted until the signallcr look
iue through the u-l,crcd aperture in the
mirror. Sees that thc CTOss-WlrcS lutcTScct the
pnint to bee si-m1llcd to. The arm Is then
clampoi. The mirror ls DOW moved round ln
altitude and aIiinuth Gin. tlc signalling key
being depressed. the reflection of The small
uusiivcrcl spot falls ou the intersection of The
cross wires. The -.luIil,r then knows chat ms
flash j., visible at the station 90 Zoe slenallrd
To-. Tine kry h. then Ulc-cd. D. springs up,
and the flash D., depressed and rendered ih-
visible tO the observer 90 the other station.
The instrument J.. now ln adlu~tmcnt ana
each time the key is depressed tine flash VIII Dc
raised to the line of thc cro---wircs and
viii hc visible, and signalling can be- done
exactly 20, with the Morse Telegraph lnhtIu-
ment, long aud short FLASHES being sent. The
motion of the sun must bc allowed TOR, ana
10 keep the dark spot on the cross wires while
the kcy j. depressed. Though not Away
necessary. % second mirror Is usually employed
when The direction OF the sun IS more than
100 from tho, luc joining Che stations, as thc
sun /. then rather behind the sCnallor, and Do
is difficult 90 send good fash without -'c-
ond mirror The flash Is, IA tim. case, sent 10y
double reflection. I'm clear weather the sig
mailing can hc read mp tO ton or twenty miles
hv the naked eye and up 90 perhaps nifty 10y
the aid OF "a telescope. The fash viii pcuc-
tratr a fair amount of haze If the distance Is
not too great.