TELEGRAPHIC APPARATUS. 
239 
insulated, we may also compensate the irregularity of the 
intervals between positive and negative currents, and obtain 
the greatest possible uniformity in the potential of the line at 
the beginning of each signal; in this way the first and last 
currents of a dot or a dash pass directly to the line, and the 
interpolated or compensating currents act upon it through a 
resistance that can be varied at will, according to the force 
required. 
A further increase of speed is obtained by interposing a con¬ 
denser between the line and the receiver; the plates of the 
condenser are themselves united through a rather large resist¬ 
ance. If a condenser were placed between the line and the 
automatic manipulator, the speed would be diminished by the 
signals running together. 
By speed is meant the number of perfectly distinct signals 
that can be transmitted in a given time, and not the interval 
required for the production of a signal. With Wheatstone’s 
apparatus, the speed is inversely as the distance, and not as the 
square of the distance. 
The following is a description of Wheatstone’s automatic 
system as used in England and France :— 
The strip of paper is prepared by an apparatus (fig. 170) called 
the perforator, consisting of three levers, one of w 7 hich produces 
two perforations in a line with each other to form a dot, while 
another makes two perforations diagonally across the strip, 
which form the dash. The third lever gives a continuous series 
of smaller perforations in the middle of the strip, and thus pro¬ 
duces a kind of rack by which a toothed wheel carries the paper 
along when the strip is placed in the automatic transmitter. 
The central perforations are made at the same time as those 
which mark the dots and dashes; the centre lever advances 
the part of the paper answering to the blank spaces. 
The transmitter is put in motion by a weight, the descent 
of which may be adjusted to send from 20 to 120 words per 
minute. The perforated paper is carried along by a toothed 
disc moved by clock-work, the teeth engaging the central per¬ 
forations against a friction roller. 
The principle according to which the alternating currents 
are produced is indicated by fig. 171. Let d be a metal disc 
divided into two parts insulated from each other, and carrying 
