AUSTIN: RESONANCE MEASUREMENTS 499 



means of making nearly all measurements depending on the de- 

 tennination of resonance. The accuracy is quite equal to that 

 obtainable with sensitive thermoelements, and greatly superior 

 to the accuracy of the detector and telephone method. ^ 



Since the audion circuit itseK is not suited to exact calibration, 

 the substitution method is generally used. The following ex- 

 amples illustrate the procedure: 



Capacity of an antenna by substitution. The antenna is loaded 

 with inductance so as to give a wave length of five to ten times 

 the fundamental, then the oscillating audion circuit is coupled 

 to the antenna inductance and the audion tuning condenser 

 varied until a cHck is heard in the telephones. In general, if 

 the couphng is close, the click will be heard at different points 

 with increasing and decreasing condenser capacity. The coup- 

 hng should then be loosened until both cUcks appear at the same 

 condenser setting, or, if this is impossible, the mean setting is 

 taken provided the points are less than a degree apart. Next, 

 leaving the audion condenser on the resonance point, the ground 

 and antenna are disconnected from the antenna inductance and 

 replaced by the calibrated variable substitution condenser. This 

 last is adjusted to resonance with the audion circuit exactly as 

 described above, and the capacity of the condenser is then equal 

 to that of the antenna, subject to a small correction for the 

 natural antenna inductance. 



Wave length of a distant station. The receiving antenna and 

 secondary oscillating circuit are first tuned exactly to the dis- 

 tant station, preferably at loose couphng, the audion tuning 

 condenser being adjusted to give the dead point of the beats 

 in the case of continuous wave reception. Next, without chang- 

 ing anything in the antenna or secondary a wave meter is coupled 

 to the secondary and adjusted to resonance by the chck method. 

 The reading of the wave meter gives at once the wave length 

 of the sending station. 



In a similar way, wave meters can be compared and condensers 

 and inductances caUbrated, either by substitution or by making 



1 Care must be taken regarding harmonics, in all measurements in which bulbs 

 are used for excitation. 



