﻿and some Applications to Physical Measurements. 493 



number of beats per second, sometimes zero, was heard. 

 The time for 20 beats was noted, the specimen then inserted 

 the new time for 20 beats being again observed, and finally 

 a third count made when the specimen was removed. The 

 note was then slightly varied and the same procedure 

 repeated. In this way from 6 to 10 readings were obtained 

 for each particular frequency used. A review of all the 

 measurements so made under conditions when the heterodyne 

 note was steady show that the greatest error incurred was 

 about 2*2 per cent. 



The wave-lengths were measured with a calibrated Towns- 

 end wave-meter, and the resonance point could be fixed to 

 within 2 metres. The shortest wave-length measured was 

 about 350 metres corresponding to a fundamental oscillation 

 in Set 2, so that the maximum error involved here is about 

 0*6 per cent. 



From all sources, then, the maximum error involved in 

 the estimation of the susceptibilities is about 3 per cent. 



The Experimental Results. 



The specimens were all prepared by Kahlbaum, Berlin, 

 and were contained in short lengths of glass tubing thus 

 permitting of quick insertion into the coil. The effect of 

 the tubing alone was found to be zero in every case. The 

 results are given below. 



I. Ferric Chloride. — The salt was examined in the form 

 of a solution in air-free water. It was contained in a closed 

 glass tube, occupied a volume 1*321 c.c. and had an approxi- 

 mate length 7*5 cm. The density was determined to be 

 1*152 gm. per c.c. at 15° C, and a volumetric estimation 

 showed that the solution contained 0*189 gm. FeCl 3 per c.c. 

 The observations are shown in Table III. 



Table III. 



Wave-length 



of Set 2 



in metres. 



Frequency 

 of Set 2 



Frequency 

 of Set 1 



Change in 

 number ©f 





Tempera- 

 ture 

 degrees C. 



per sec. 

 N. 



per sec. 



beats per sec, 

 p=2dn. 



j,/N. 





xlO 5 



XlO 5 





xio~ 6 





372 



8-07 



403 



2-59 



3-21 



15 



385 



7-80 



3-90 



2-49 



3-19 



15 



400 



7-50 



3 75 



2-39 



3-19 



15 



418 



7-18 



3-59 



2-29 



319 



15 



Mean y,/N = 3-19x lO" 6 at 15° C. 



