A self-balancing line-reversal pyrometer has been developed to measure gas temperatures above about 1200°C (1500°K). The basis of the line-reversal method is widely known, and some particular aspects have been described previously. The present apparatus can be used to follow variations in flame temperature; a signal proportional to the temperature is displayed on a chart recorder. The pyrometer has been used to record the temperature of a fluctuating sodium-seeded flame with an estimated accuracy similar to that of a manually operated system, i.e. to ± 1% at about 2000°C (2300°K).