§ Mr. HOBHOUSE
In the more modern telephone exchange systems stronger electric currents are used than formerly in order to obtain quicker communication and clearer speech. The drawback to these systems—which are worked on the central battery principle—is that if the receiver is kept close to the ear at the moment when the current is turned on or off the resulting click of the diaphragm is disagreeable. Subscribers soon learn, however, not to put the receiver close to the car while communication is being established or broken. The central battery system referred to is in use in all the principal exchanges in the London area and at most of the chief provincial exchanges. It is also generally used in the United States and on the Continent.