200 Proceedings of Royal Society of Edinburgh. [sess. 
beneatli the lever and parallel to it, zz. Below the pulley round 
which the cord passed, there is an electro-magnet, and the pulley is so 
attached to the keeper of the magnet as to be oblique. When the 
magnet is not acting, the keeper is free, the lower cord touches the 
roughened drum, and the latter moves in a given direction. If, 
however, the magnet acts, the keeper bearing the pulley is pulled 
to one side so as to bring the upper cord against the roughened 
drum, and the latter moves in the opposite direction. Thus the 
movement of the screw by which the aluminium lever may be 
raised or depressed is regulated by the roughened drum, and this 
again by the electro-magnet and the two cords. Finally, the 
electro-magnet is brought into action when the platinum wire on 
the aluminium lever dips into the mercury. This diverts a portion 
of the current that drives the paper feeder into the electro-magnet, 
the latter then acts and the upper cord is brought into play. The 
following is an account exactly of what occurs : — 
1. When the reproducing point connected with the aluminium 
lever sinks too low, the wire attached to the lever dips in the 
mercury; the current is made, the armature is drawn forwards, 
the upper cord presses on the rough cylinder, the cylinder with the 
screw turns in a direction against that of the hands of a watch, 
the bearer of the lever and the reproducing point are lowered ; the 
reproducing point pressing on the cylinder, therefore, lifts the lever, 
and the free end of the lever is raised. Again 
2. When the reproducing point rises too high, the wire attached 
to the lever is lifted out of the mercury, the current is broken, the 
armature falls away by the action of a counterpoise, the lower cord 
presses on the rough cylinder, the cylinder and screw are turned 
in the direction of the hands of a watch, the bearing apparatus is 
raised, the recording point on the aluminium lever is relatively 
lowered, and the free end of the lever falls. 
By this arrangement, which may be called an automatic “ finger 
and thumb ” for turning the screw in reverse directions, there is a 
constant self adjustment according to the depth of the grooves on 
the wax cylinder, which, again, corresponds with the varying 
intensity of the sounds. 
