A resistance box arranged so that the coils may be plugged in multiple
instead of in series. Such can be used as a rheostat, as the resistance
can be very gradually changed by putting the coils one by one into
parallel with each other. Thus by adding in parallel with a 10 ohm coil
a 10,000 ohm coil the resistance is decreased to 9.999001 ohms, and thus
the resistance can be very slowly changed without sudden stops or abrupt
changes.

[Transcriber's note: The correct value is 9.99001]