, 1875-08-14
4g<.gar1 hrg q. III n e.
TALKING BY FLASHES OF LIGHT.
PIE (FrOm the SpGtator.I

sailor and the surveyor as to the position and
direction of particular rocks, headlands,
mountains, and so forth, they have never been
applied, except in the shape of beacons carry.
ing an already expected bit of intelligence from
hilltop to hill-top, to enable distant persons to
communicate with each other. Probably the
reason has been that it has hitherto been
thought impossible to ensure that the informa-
ton which is thus communicated from any
particular centre of light shall actually reach
the destination for which it is intended, and
that the sender shall receive back a reply. 1t
is not very encouraging work to send out mes
sages into space, on the chance that they will
reach the proper person and be by him under
stood. Advertising in the agony column"
of the Times, on the chance that thu person
aimed at, whose proper address you don't know,
will read what you advertise, is a hopeful pro-
cess, compared with flashing out messages 10
sea or land without any reasonable ground for
belief that their meaning is caught by any per-
son to whom the intelligence it contains would
be of use. However, Mr.. Henry O. Nance, Of
the Government Persian Gulf Telegraph De-
partment, appears to have completely got over
this difficulty, by the invention of the ingenious
little instrument explained by Mr.. Samuel
GOOde, in the admirable lecture which he
delivered at the Royal United Service Institu.
ton on Monday, the 14th inst. The instru-
ment, which Mr.. Nance has called a Hello
graph, but which might just as we'll be called
a selenograph or lampadograph, since it en-
ables the person who uses it to signal with any
light bright enough to be reflected to the need
full distance, is simply a little mirror, the in
O~lination of which can be so altered, even by
a hair's-breadth, in any plane, as to enable the
person who uses it to reflect a ray Of light from
its surface precisely in a given line of direction.
1tdoes not matter whether the place to which
the message is to be sent can be seen at the
moment or not. Of course, if the place be at
all far off, and the message be sent by artif-
cial light at night, it would be impossible to
see the destination of the message. Still, if in
the daytime, when the place was visible, the
precise direction requisite for the ray to travel
in order to reach its destination had been as.
c%ertained, there will be no manner of difficulty
in sending it off IN that direction, even at a
time when you are quite unable to see the
goal to which you are sending it. All you
need to assure you of its arrival, and to obtain
a reply, is the appearance Of a star Of light in
the Line in which you have transmitted your
own ray,-which star is perceived through a
minute transparent spot of your mirror, from
which the silver has been rubbed off That
signal once received, the communication is
established, and nothing is easier than to con-
verse with your distant correspondent. This
is done by means of the system known as the
Morse system of Telegraph, a system which
expresses all the letters Of the alphabet by
means OF different combinations of a dot and a
line. When using light signals, the dot is re-
presented by an instantaneous fash aud disap-
pearance of the star, the line by a somewhat
longer apparition of it. And by the aid Of this
very simple language, any two persons whose
mirrors can carry Il flash over the distance
between them may converse at wilt for any
time during which their lights serve thom.
But how far can signals of this kind be per-
oeived2 The answer is, Of course, that this
depends very much on the light used. With
q bright sun and q t~olerably good altitude,
there seems no sort of difficulty 10 conversing
atthe distance of fifty miles; and with strong
mirrors and much more elevated stations, such
as. the tops Of really high mountains, like
Mont Blanc, for example, We can see no
reason why a very much longer raOge indeed
could not easily be attained. In India it ap,
pears that Captain Oollette, deputy-assistant-
quartermaster-genera has reported from Sim
lagthatfal "the reports of the work ofthe hello
graph except one Ito be noticed subsequently,
are favourable. and all agree on the following
points : (a) that signals given by it are
perfectly clear and satisfactory; (6) that they
can easily be used 10 ordinary weather, with
out telescopes, up to fifty miles," And the
instrument by which these results are attained
can b@ made for a sum not exceeding &5
sterling, and Of weight not exceeding 5 10.
axoifdupois. With the use of a telescope, of q