ON HUNTING TELEGRAPHS. 
•301 
The practical difficulties of the system, simple as it may 
have seemed from the foregoing* description, are very great. 
It is of course necessary that the markers at the two stations 
shall move with perfect uniformity, as if connected firmly 
together. The slightest difference in the speed of the two 
would be fatal. The colour is apt to run on the damp paper, 
and as the current on a long wire does not cease at the moment 
at which battery contact is broken, the marks as received are 
apt to be rather longer than those of the original, so as to 
merge one into the other. 
The apparatus at all the stations is precisely similar. A 
massive iron frame carries a pendulum about six feet long 
having a very heavy iron bob, whose movements are controlled 
by electro-magnets, which attract it at each oscillation and 
hold it fast until the current which magnetizes them is cut off 
by a regulator clock, the going of which can be controlled with 
the greatest nicety without stopping it. The large pendulum, 
whose beats exactly correspond with those of the regulator, 
gives motion to two curved tables, one on each side, on which 
the prepared paper or original despatch is laid. The metal 
tracers or pencils are fixed above these tables in such a manner 
that they pass over the paper as it moves, ruling a line at each 
vibration of the pendulum. The pencils are connected with 
screws which move them the ninetieth of an inch between each 
vibration, so as to rule a series of lines a ninetieth of an inch 
apart. They cannot be arranged so as to pass over the paper 
in both directions without tearing it, and are therefore lifted 
alternately. To avoid loss of time from this arrangement, 
two despatches are transmitted at the same time, one while 
the pendulum swings to the right, the other while it moves to 
the left. The clocks at the two stations are kept in perfect 
accord by altering their rate during the progress of the trans- 
mission, in such a manner that a straight line which is ruled 
at the edge of the original despatch shall be reproduced on 
the receiving-paper. In the plate we give fac-simdes of mes- 
sages in Persian and in English, which were transmitted from 
Liverpool to London. 
In CasehTs system the synchronism of the two sets of 
apparatus in correspondence must be perfect ; and as only the 
ninetieth of an inch of the despatch is traced by one move- 
ment of the pencil, its transmission is not very rapid. Only 
one line-wire is required. 
In the telegraph now working between Liverpool and Man- 
chester, Bonelli uses a sufficient number of pencils, arranged 
in form of a comb, to copy the whole despatch by a single 
movement, and thus not only saves time, but, as perfect 
synchronism is unnecessary, avoids the necessity for elaborate 
arrangements for regulating the speed of the apparatus. 
