HERTZIAN ^YAYE ^\ IRE LESS TELEGRAPHY. 201 



minimum inductance, the character of the current flow changes, and 

 it becomes intermittent, and the cell acts as an interrupter, the current 

 being interrupted from 100 to 2,000 times per second, according to the 

 electromotive force, and the inductance of the circuit. Under these 

 conditions, the cell produces a rattling noise and a luminous glow 

 appears round the tip of the platinum wire. Thus, in a particular case, 

 with an inductance of 0.004 millihenry in the circuit of a Wehnelt 

 break, no interruption of the circuit took place, but with one millihenry 

 of inductance in the circuit, and with an electromotive force of 48 

 volts, the current became intermittent at the rate of 930 per second, 

 and by increasing the voltage to 120 volts, the intermittency rose to 

 1,850 a second. 



The Wehnelt break acts best as an interrupter with an electromo- 

 tive force from 40 to 80 volts. At higher voltages a third stage sets 

 in: the luminous glow round the platinum wire disappears, and it 

 becomes surrounded with a layer of vapor, as observed by MM. Violle 

 and Chassagny; the interruptions of current cease, and the platinum 

 wire becomes red hot. If there is no inductance in the circuit, the 

 interrupter stage never sets in at all, but the first stage passes directly 

 into the third stage. In the first stage bubbles of oxygen rise steadily 

 from the platinum wire, and in the interrupted stage they rise at 

 longer intervals, but regularly. The cell will not, however, act as a 

 break at all unless some inductance exists in the circuit. 



In applying the Wehnelt break to an induction coil, the condenser 

 is discarded and also the ordinary hammer break, and the Wehnelt 

 break is placed in circuit with the primary coil. In some cases, the 

 inductance of the primary coil alone is sufficient to start the break 

 in operation, but with voltages above 50 or 60, it is generally neces- 

 sary to supplement the inductance of the primary coil by another 

 inductive coil. The best form of Wehnelt break for operating induc- 

 tion coils is the one with multiple anodes (see Dr. Marchant, The 

 Electrician, Vol. XLII, page 841, 1899), and when it has to be used 

 for long periods, the kathode may advantageously be formed of a 

 spiral of lead pipe, through which cold water is made to circulate. 



Another form of electrolytic break was introduced by Mr. Cald- 

 well. In this, a vessel containing dilute sulphuric acid is divided 

 into two parts. In the partition is a small hole, and in the two 

 compartments are electrodes of sheet lead. The small hole causes an 

 intermittency in the current which converts the arrangement into a 

 break. Mr. Campbell Swinton modified the above arrangement by 

 making the partition to consist of a sort of porcelain test-tube with 

 a hole in the bottom. This hole can be more or less plugged up by 

 a glass rod drawn out to a point, and this is used to more or less close 

 the hole. This porcelain vessel contains dilute acid and stands in a 



