with Mercury contained in Tubes. 519 



were : (a) lead glass, 4 cm., 5"8 mm., *26 mm., 1 ohm ; 

 (b) quartz, 3*7 cm., 5'3 mm , "22 mm., 38 ohms ; (c) quartz, 

 3 cm., 5*3 mm., '3 mm., 2 ohms ; (d) quartz, 35 cm., 4 mm., 

 *46 mm., 5*25 ohms. 



Effect of Resistance of Circuit on Frequency. 



The frequency is not greatly affected by changing the 

 external resistance in the fan effect. Tims in a series of 

 experiments with a quartz tube (11 cm., 5'3 mm., '35 mm., 

 95 volts) the resistance in series with the tube was changed 

 step by step from 12 to 111 ohms. The frequency rose from 

 34 to 39. The effective resistance of the tube (calculated 

 from the mean current observed) rose meanwhile from 240 

 to 570 ohms. 



Experiments with Self-induction in Series with the Tube 



Hitherto the self-induction in the circuit has been reduced 

 as far as possible. If the circuit is made inductive, interesting 

 intermittent luminous effects may be obtained by the use of a 

 few accumulators only. 



Gernsback (Scientific American, xciii. p. 82, July 29th, 

 1905) has described an apparatus of this type intended as an 

 interrupter for small induction-coils. A glass capillary 

 U-tube of 1/8 mm. bore is provided with enlarged ends, 

 filled with pure mercury and immersed in water. With 4 to 

 6 volts this tube acts as an interrupter and gives a high- 

 frequency note. It allows from '25 to '5 ampere to pass, 

 and was used in connexion with the condenser of the coil. 

 Higher voltages caused the interrupter to work irregularly. 



Experiments in which the self-induction of the circuit is 

 large are not always successful : great care must be taken to 

 rid the tube and mercury of foreign matter. A soda-glass 

 tube (10 cm., 7 2 mm., -97 mm.) was set up with the bottles 

 serving as mercury reservoirs as usual. After running for 

 some time without self-induction, on three large accumulators 

 in series, it had a period of about 30 seconds, during a third 

 of each period the column was unbroken. A resistance of 

 one-tenth of an ohm wound non-induclively was removed 

 from the circuit, and an inductive coil of the same resistance 

 wound on laminated iron inserted in its place. This iron 

 formed an open magnetic circuit for the coil, the self- 

 induction of which, measured with an alternating current of 

 about five amperes (frequency 60) was 2*5 millihenries. The 

 central part of the tube lit up brilliantly on inserting the self- 

 induction, but the light ceased after a few seconds, and left 



2M2 



