TELEGRAPHIC APPARATUS. 
2 33 
often to readjust the apparatus according to the state of the 
line, and this occasions loss of time and other inconveniences. 
Brown and Allan have invented a relay, which by a peculiar 
arrangement of the armature, may be so adjusted as not to be 
affected by the variations of the current in its circuit. In this 
relay, the contact is not directly made by the moving slip, which 
Fia. 166, 
is kept in equilibrium between two opposing spiral springs. 
When the slip has been attracted to one side by the line current, 
it tends to revert to its normal position when the current ceases 
or diminishes; but if the currents follow one another very 
rapidly, it is attracted again before it has got completely back ; 
the charge and discharge of the line are therefore indicated by 
oscillations of the slip, which, however, remains the more distant 
from its normal position in proportion to the power and rapidity 
of succession of the currents. 
