Resistance Box.
A box filled with resistance coils. The coils are connected in series so
that a circuit including any given number has their aggregate resistance
added to its own. The terminals of consecutive coils are connected to
short blocks of brass which are secured to the top of the box, lying
flatwise upon it, nearly but not quite in contact with each other. Plugs
of brass are supplied which can go in between pairs of blocks, which
have a pair of grooves reamed out to receive them. Such plugs short
circuit the coil below them when in position. The cut shows how such
coils are connected and the use of plugs to short circuit them. The
diagram shows the top of a Wheatstone bridge, q. v., resistance box with
connections for determining resistances.
Fig. 291. RESISTANCE BOX.
Resistance Box, Sliding.
A resistance box whose coils are set in a circle. Two metal arms with
handles are pivoted at the centre of the circle and by moving them
around they make and break contacts so as to throw the coils in and out
of circuit. The object is to permit an operator to adjust resistance
without looking at the box--an essential in duplex telegraphy.
Resistance, Breguet Unit of.
The same in origin as the Digney Unit. (See Resistance, Digney Unit of.)
It is equal to 9.652 Legal Ohms.
Resistance, Carbon.
A resistance, a substitute for a resistance coil; it is made of carbon,
and is of various construction. In the Brush dynamo regulator a set of
four vertical piles of plates of retort carbon, q. v., is used as a
resistance, whose resistance is made to vary by changing the pressure.
This pressure automatically increases as the current strength increases,
thus reducing the resistance.