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In the F�ry radiation pyrometer this difficulty is obviated, as the instrument may be placed at a considerable distance from the furnace.

Many attempts have been made to determine flame temperatures by means of thermo-electric couples and by radiation pyrometers.

The pyrometers used at present are the Wanner optical pyrometer and the Fery radiation pyrometer.

The Measuring of Temperatures.—At present the only possible known method of measuring the temperature of the furnace gases is by optical and radiation pyrometers.