164 DRS. GUY BARLOW AND H. B. KEENE ON THE ANALYSIS OF SOUND. 
Plotting aja m against p/n 0 we obtain the response curve (eequation y — - 
\ 1 
shown by the full line in fig. 15. The amplitude falls to half value when p = 
+ ®7 
± 
Fig. 15. Response curve. 
i.e. when the difference in frequency between interrupter and current is equal to the 
natural frequency of the galvanometer. 
[For the galvanometer with period 3 sec. used in the experiments the half-value 
amplitude is given for a true frequency of -J/sec., or the “ width of response ” is f/sec. 
The true frequency of the forced motion of this galvanometer over the range of the 
response is indicated on the lower scale in fig. 15.] 
Resolving Power .—Consider first the case of two equal components. Let 
a m — maximum amplitude for each separately, 
q = frequency difference, 
a u a 2 = response amplitude, for one component alone, at frequencies \q and q respec¬ 
tively from the maximum. 
The superposition of the two response curves is shown in fig. 16. The degree of reso¬ 
lution is determined by the ratio 
_ amplitude at central dip 
amplitude at summit on either side ' 
2 
d - 
Approximately this ratio is 
, neglecting a slight displacement of the maxima. 
