IXTKHACTION OF POLYMERS AXD MECIIAMCAL WAVES 



335 



78,930 



78,920 



> O 



o u 



Z UJ 



78,910 



3^ 78,900 - 



U: 78,890 



78,870 



45 



50 



5 10 15 20 25 30 35 40 



TEMPERATURE IN DEGREES CENTIGRADE 



Fig. 10 — Temperature variation of resonant frequency before and after add- 

 ing weights to mounting wires. 



(or dilute polymer solution) is bothersomely small. An excellent oscillator 

 at 20 kc can hardly be expected to drift less than ±2 cycles, but at 20 

 kc the A/ like that between the sets of curves on Fig. 10 might be only 

 10 cycles, so 20 to 35 per cent error could come in. Hence, a different 

 scheme for measurement of ju than that in earlier systems ' was 

 evolved. The tenth harmonic of the (say 80 kc) resonant frequency was 

 beat against the 79th harmonic of a controlled standard 10-kc frequency. 

 An interpolation oscillator accurately readable to 1 cycle then supplies 

 the many hundred (roughly 1000) difference between these two high 



90,000 



70,000 



(^ 60,000 

 m 2400 



10 15 20 25 30 35 40 



TEMPERATURE IN DEGREES CENTIGRADE 



Fig. 11 — Temperature variation of resistance at resonance before and after 

 adding weights to mounting wires. 



