PIERCE. — OSCILLATIONS OF A HERTZ OSCILLATOR. 



327 



c 



Figure 2. Coil and suspended 

 disc of the high-frequency dy- 

 namometer. 



The action of the instrument is as follows : Oscillations in the coil 

 induce oscillations in the disc, and between these two sets of oscilla- 

 tions there is a force which causes the 

 disc to tend to set itself at right angles 

 to the plane of the coil. A mathemati- 

 cal theory of the instrument, together 

 with some experiments showing that the 

 deflections of the disc are proportional 

 to the square of the current in the coil, 

 is given by me in volume 20, page 226, 

 of the Physical Review for 1905. 



In place of the dynamometer, a 

 Geissler tube, connected to the two sides 

 of the condenser, was used in some of 

 the experiments. 



The Calibration of the Wavemeter. — 

 For wave-lengths greater than 350 



meters, I have a set of standard oscillators 

 whose periods have been determined by 

 spark-photographs taken with the revolv- 

 ing mirror. 2 These could, however, not 

 be employed in the present experiments, 

 where the greatest length of oscillator 

 that could be set up in the room had a 

 wave-length of only 63 meters. It was, 

 therefore, necessary to use another method 

 of calibrating the wavemeter of Fig. 1 ; 

 namely, by tuning it to resonance with 

 an oscillator consisting of various lengths 

 (4 to 17 meters) of two parallel wires, 

 1 mm. in diameter and 8 cm. apart. It 

 was assumed that the wave-length of such 

 a parallel-wire oscillator is four times the 

 length of one of the wires. This assump- 

 tion is on the supposition that there is a 

 loop of potential at the free end of the 

 oscillator, and that the velocity of the 

 waves on parallel wires is equal to the 

 velocity of light. 



In regard to the loop at the free end, Bumpstead 3 has shown that 

 this loop of potential for a parallel-wire oscillator is really beyond the 



Figure 3. Mounting of 

 dynamometer with variable 

 sensitiveness. 



Phys. Review, 1907, 24, 152. 



3 Am. Jour. Sci., 1902, 14, 359. 



