332 C. Barus — Effect of Temperature and of Moisture 



earlier papers.* The slender condenser, KK, was effectively 

 50 cm long, -32 cm in internal, and '60 cm in external diameter. 

 The inner face (surface of the rod cd) is charged to about 40 

 volts. The tube KK, insulated at the ends from the rod, is 

 put to earth at E. The electrical discharge takes place radially 

 from rod to tube, and should occur only when the emanation 

 passes in the cylindrical shell between the faces (-14 cm thick 

 and 50 cm long) entering at b and leaving at a. It is difficult in 

 so slender an apparatus and in view of the use made of it to 

 avoid conduction through the insulators, altogether, particu- 

 larly in a damp atmosphere. Hence in the following tables 

 the insulation when the medium is ordinary air, is given ; but 

 even if ignored it will not probably affect the relation to tem- 

 perature. In a warm dry room the insulation is perfect, and 

 advantage was frequently taken of this observation. 



A steam or water jacket, «/, surrounds the condenser for 

 special experiments. § 22. Steam enters and leaves by the 

 tubulures, s. 



9. Method. — The method consisted in reading the efflux 

 volumes, Y, at the gasometer or aspirator bottle, before and 

 after the series of electrical measurements. As the latter 

 were always duplicated, three volume measurements were 

 made at stated times. From these dV/dt was obtained graph- 

 ically. 



The fall of potential at the electrometer (capacity of the 

 latter 60 cm , in parallel with that of the condenser, 89 cm ) was 

 observed at intervals of 15 seconds apart. Eight readings in 

 two series were made between the volume readings. The 

 initial potential being about 41 volts, and equivalent to 8T or 

 80 scale parts, respectively, each scale part is equivalent to 

 about half a volt; but the absolute values are without interest. 

 As usual, care was taken to await constancy of temperature in 

 the water bath. 



10. Data. —In the following Table II, the time of observa- 

 tion in minutes, t, the reading of the gasometer, V, in liters, 

 the reading of the electrometer in scale parts, s (zero at s=250), 

 and the temperature, 0, of the water bath are given in succes- 

 sive columns. In the second and third columns, moreover, the 

 rate of efflux of the air, d V/dt, in liters/min., and the initial 

 radial electrical currents ds/dt are tabulated. E is the initial 

 potential difference in volts. 



As a rule, two values of d V/dt are entered for each tem- 

 perature, one for a moderate current of about '50 liter/min. 

 through the condenser and the other for the stronger current 

 of about 1-0 liter/min. From brevity, an example of these 

 data corresponding to a single temperature, 6 = 15'3°, will only 

 be given. 



*This Journal (4), xi, p. 310, 1901 ; Phil. Mag. (6), vol. i, p. 572, 1901; ibid. 

 (6), ii, p. 40, 1901 ; and elsewhere. 



