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Dr. J. X. Pring and Mr. A. Parker on the 



accurately measured than in previous work, to extend these 

 up to about 2000°, and, at the same time, to notice what 

 influence is exerted by the pressure of the surrounding gas 

 and the condition of the carbon. oSTo attention seems to 

 have been paid by previous workers to the chemical purity 

 of the carbon. 



The npparatus used in the present work (fig. 1) was 



Fio-. 1. 



designed primarily for examining the phenomena at the 

 anode during the discharge with high currents, and consisted 

 of a tubular glass flask, in which a carbon rod (A) was 

 supported by inserting in the graphite plugs B, B, which 

 themselves were soldered into the water-cooled brass tubes 

 C, C. An air-tight joint was made at D, D, by means of 

 soft wax. The water-cooled tubes served for leading in the 

 current which was used to heat the carbon. The carbon rod 

 used was 5*1 cm. long and O50 mm. diameter, or 8*01 

 sq. cm. surface. This arrangement of the apparatus enabled 

 the rod to be heated to 2200°. 



Temperature Readings. — Accurate temperature readings 

 were taken with a Wanner optical pyrometer. Tnis was 

 directlv calibrated n gainst a standardised thermocouple up to 

 1400°, and at the "black body" melting-point of platinum. 

 1545° *, and as carbon has been found to radiate approxi- 

 mated as a "black body," the temperature readings will 

 * Holborn and Heiming, Sitzungsber. I: Acad. JViss. Berlin (1905) 

 xii. p. 311. 



