abstract:In telephony, ringdown is a method of signaling an operator in which telephone ringing current is sent over the line to operate a lamp or cause the operation of a self-locking relay known as a drop. Ringdown (a) is used in manual operation, as distinguished from dialing, (b) uses a continuous or pulsed ac signal transmitted over the line, and (c) may be used with or without a switchboard.
Using the cavityringdownmethod and Changing the used mirrors, wemeasuredthereflectivity of fourmirrorsunder the ordinary condition and obtained the absorptionof the cavity.