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from the Louvre, which he repeated with 
liis own machine; and this was again re- 
peated from the next height, with incon- 
ceivable rapidity, to the final station at 
Lisle. 
Various experiments ivere in consequence 
tiied upon telegraphs in this country ; and 
one was soon after set up by government, 
in a chain of stations from the Admiralty 
office to the sea-coast. It consists of six 
octagon boards, each of which is poised 
upon an axis in a frame, in such a manner 
that it can be either placed vertically, so 
as to appear with its full size to the obser- 
ver at the nearest station, or it becomes in- 
visible to him by being placed horizontally, 
so that the narrow edge alone is exposed, 
which narrow edge is from a distance invisi- 
ble. .Six boards make thirty-six changes, 
by the most plain and simple mode of work- 
ing; and they will make many more if more 
iwere necessary : but as the real superiority 
of the telegraph over all other modes of 
making signals consists in its making letters, 
we do not think that more changes than 
the letters of the alphabet, and the arith- 
metical figures, are necessary ; but, on the 
contrary, that those who work the tele- 
graphs should avoid communicating by 
words or signs agreed upon to express sen- 
tences ; for that is the sure method never to 
become expert at sending unexpected in- 
telligence accurately. This telegraph is, 
without doubt, made up of the best number 
of combinations possible ; five boards would 
be insufficient, and seven would be useless. 
It has been objected to it, however, that its 
form is too clumsy to admit of its being 
raised to any considerable height above the 
building on which it stands;. and that it 
cannot be made to change its direction, 
and consequently cannot be seen but from 
one particular point. Several other tele- 
graphs have been proposed to remedy these 
defects, and perhaps others to w'liich the 
instrument is still liable. The dial-plate of 
a clock would make an excellent telegraph, 
as it might exhibit one hundred and forty- 
four sign-s, so as to be visible at a great dis- 
tance. A telegraph on this principle, with 
only six divisions instead of twelve, would 
be simple and cheap, and might be raised 
tweiity or thirty feet high above the build- 
ing without any difficulty : it might be sup- 
ported Oil one post, and therefore turn 
round ; and the contrast of colours would 
always be the same. 
TELESCOPE, au optical instrument, 
which is used for discovering awl viewing 
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distant objects, either directly by glasses, 
or by reflection. Telescopes are either re- 
fracting or reflecting ; the former consist of 
different lenses, through which the objects 
are seen by rays refracted by them to the 
eye ; and the latter, of specula, from which 
tlie rays are reflected and passed to the eye- 
The lens, or glass, turned to the object, is 
called the object-glass ; and that next the 
eye, the eye-glass ; and when the telescope 
consists of more than two lenses, all but 
that next tlie object are called eye-glasses. 
The principal effects of telescopes de- 
pend upon this maxim, “ that objects ap- 
pear larger in proportion to the angles 
which they subtend at the eye ; and the ef- 
fect is the same, whether the pencils of 
rays, by which objects are visible to us, 
come directly from the objects themselves, 
or from any place nearer to the eye, where 
they may have been united, so as to fonn 
an image of the object; because they issue 
again from those points in certain direc- 
tions, in the same manner as they did from 
the corresponding points in the objects 
themselves. In fact, therefore, all that is 
effected by a telescope, is first to make 
such an image of a distant object, by means 
of a lens or mirror, and then to give the 
eye some assistance for viewing that image 
'as nearws possible ; so that the angle, which 
it shall subtend at the eye, may be very 
large, compared with the angle which the 
object itself would subtend in the same si- 
tuation. This is done by means of an eye- 
glass, which so refracts tlie pencils of rays, 
as that they may afterwards be brought to 
their several foci, by the natural humours 
of the eye. But if the eye had been so 
formed as to be able to see the image, with 
sufficient distinctness, at the same distance, 
w'ithoiit an eye-glass,' it would appear to him 
as much magnified, as it does to another 
person who makes use of a glass for that 
purpose', though he would not, in all cases, 
have so large a field of view. 
Although no image be actually formed 
by the foci of the pencil without the eye, 
yet if, by the help of an eye-glass, the pen- 
cils of rays shall enter the pupil, just as 
they would have done from any place with- 
out the eye, the visual angle will be the 
same as if an image had been actually form- ' 
ed in that place. 
Telescopes are of several kinds, distin- 
guished by the number and form of their 
lenses, or glasses, and denominated from 
their particular uses, &c. such are the 
“ terrestrial, or land telescope,” the “ celes- 
