TELEGRAPHIC APPARATUS . 
243 
current is sent into the line. Where the paper is perforated, 
a dot gives a reversed current at each oscillation, and a dash 
at each second oscillation. The rod M passes through the 
upper perforation, and the reversed current passes to the 
line. 
The transmitter can be adjusted to work at the maximum 
speed of 130 words; but this does not mark the absolute speed 
at which the apparatus can work. This speed is rather deter- 
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Fig. 174. 
mined by the receiving capacity of the registering apparatus, 
and this capacity is limited, not only by the mechanical inertia 
of the apparatus itself, but also by what may be termed the 
inertia of the electro-magnet. Thus the speed of transmission 
is limited by the capacity of the receiver. 
This last is a very sensitive Morse printer. The paper 
passes above the printing disc with a uniform velocity, and the 
apparatus is so arranged that it can be adjusted to print at 
any speed from between 20 and 130 words per minute. The 
disc is fixed on an axle moved by clockwork, and turns partly 
in the groove of a roller of larger diameter, which dips into 
