Now slowly raise the bridge current, watching the meter. it will at first go off scale to the right. This is because a thermistor has a resistance much higher than the other bridge rms, which are each 1kΩ. As the current is raised, heating of the thermistor decreases its resistance, until eventually the bridge will pass through balance, shown by the meter needle moving to the left.
Adjust the bridge current until the meter needle is central.