554 BIOLOGICAL EFFECTS OF RADIATION ' 



accomplish this by providing an ammeter to read the current flowing to 

 the condenser plates; and were the frequency low enough, this would 

 be entirely practical (calculation of voltages from capacity reactance 

 of the condenser). However, at the extremely high frequencies used in 

 biological work accurate current-measuring instruments are not avail- 

 able, and it is necessary to arrive at some approximation by other means. 

 One method is to expose a column of neon gas to the dielectric field of the 

 condenser. At the fixed frequency used in any one series of experiments, 

 it is found that increasing or decreasing the field of the condenser raises 

 or lowers the height of ionization in the gas column. At a fixed frequency 

 the indications are found to be quite sharp and it is possible by this means 

 reasonably to standardize the dosages. This principle has lately been 

 applied to volume indicators on radio-broadcast receivers where it is 

 again used as a voltage-indicating device. It is quite true that such a 

 device absorbs power from the oscillatory circuit and this power must 

 be made available in addition to that required by the biological material. 



PUSH-PULL OSCILLATOR 



In Fig. 3 is described a high-frequency push-pull oscillator using recti- 

 fied-alternating-current power supply. Two UX210 7>^-watt tubes 

 supply power to the oscillating circuit L1-L2. L1-L2 are made of ji-in. 

 copper tubing formed into a half circle connecting the grids and the plates 

 of the tubes. The radius of this circle is approximately 6 in. Midway 

 along the two conductors are connected choke X2 and resistor Rl. 

 Choke X2 is a coil of 100 turns of No. 38 D.C.C. wire wound on a tube 

 1 in. in diameter. Resistor Rl is inductively wound and has a resistance 

 of approximately 10,000 ohms. The four chokes, XI, in the filament 

 circuit of the tubes are made of 10 turns of No. 14 wire on a core 1 in. in 

 diameter and the turns are spaced the diameter of the wiring. By-pass 

 condensers CI are small mica condensers having a value of 2,000 fx/xi. 

 Resistor R2 provides the filament center tap and is a General Radio 

 type 437, having a total resistance of 60 ohms. By-pass condenser C4 

 has a value of 2,000 nnL, and is of sufficient voltage rating to stand the 

 voltage of the power supply. Resistance RS is a voltage divider resist- 

 ance across the D.C. output of the high-voltage vacuum-tube rectifier 

 and is a General Radio type 446. The resistance is approximately 

 15,000 ohms. Condensers C2 and X3 comprise the 120-cycle filter in 

 the vacuum-tube rectifier output. Condensers C2 have a value of 8 /xf- 

 each and X3 a value of 20 h. at 50 ma. This rectifier filter is known as a 

 General Radio type 527-A. A UX280 full-wave rectifier tube is used 

 for rectification. Transformer Tl supphes the A. C. voltages for the 

 rectifier and for the filament circuit of the oscillator tubes and the recti- 

 fier tube. This transformer is a General Radio type 565-B, rated at 200 

 watts with a high-voltage output of 600 volts each side of the center tap. 



