Key, Plug.
An appliance for closing a circuit. Two brass blocks are connected to
the terminals, but are disconnected from each other. A brass plug
slightly coned or with its end split so as to give it spring action is
thrust between the blocks to complete the circuit. It is used in
Resistance coils and elsewhere. (See Coil, Resistance.) Grooves are
formed in the blocks to receive the plug.
Key, Reversing.
(a) A double key, arranged so that by depressing one key a current flows
in one direction, and by depressing the other a current flows in the
opposite direction. It is used in connection with a galvanometer in
experimental, testing or measuring operations.
(b) A key effecting the same result used in quadruplex telegraphy.
Key, Sliding-Contact.
A name given to the key used for making instantaneous contacts with the
metre wire of a metre bridge, q. v. The name is not strictly correct,
because it is important that there should be no sliding contact made, as
it would wear out the wire and make it of uneven resistance.
It is a key which slides along over the wire and which, when depressed,
presses a platinum tipped knife edge upon the wire. On being released
from pressure the key handle springs up and takes the knife edge off the
wire. This removal is essential to avoid wearing the wire, whose
resistance per unit of length must be absolutely uniform.
Key, Telegraph.
The key used in telegraphy for sending currents as desired over the
line. It consists of a pivoted lever with finger piece, which lever when
depressed makes contact between a contact point on its end and a
stationary contact point on the base. This closes the circuit through
the line. When released it springs up and opens the line circuit.
Kilo.
A prefix to the names of units; it indicates one thousand times, as
kilogram, one thousand grams. A few such units are given below.
Kilodyne.
A compound unit; one thousand dynes. (See Dyne.)
Kilogram.
A compound unit; one thousand grams; 2.2046 pounds avds.