At small country towns or villages, where the message traffic is light, the Wheatstone " A B C " instrument is used.
In this apparatus electric A B C currents are generated by turning a handle (placed in front of the instrument), which is geared, in the instru ment.
A noticeable feature in the modern A B C indicator, as well as in all modern forms of telegraph instruments, is the adoption of " induced " magnets in the moving portion of the apparatus.
At offices where the work is heavier than can be dealt with by the A B C apparatus, the " Single Needle " instrument has been very largely employed; it has the advantage of slight Single liability to derangement, and of requiring very little adjustment.
The cheek-teeth (premolars and molars) form a A B C FIG.
