138 Lord Rayleigh and Dr. A. Schuster. [May 5 5 



128-179 

 •180 

 •181 

 •179 

 •174 

 •180 

 •189 

 •185 



The small discrepancies would very likely be still further reduced 

 if greater care was taken to ascertain the exact temperature of the 

 fork. As a mean of different sets we find, 



Number of vibrations in 1 second=128-180 for t = VS°°0 C. 



128-161 t=U°-6 C. 



From these data and the number of beats counted during each 

 coarse of experiments we can, with the necessary accuracy, determine 

 the number of vibrations of the fork, which served to regulate the 

 velocity of the revolving coil. 



Calculation of Results. — For accurate calculation, the expansion 

 given in the Report of the British Association is not sufficient. 

 Instead of taking into account a greater number of terms, we may 

 with equal facility have recourse to the original quadratic equation for 

 the resistance. We find 



R= ~ J ^1* C °-t(ft [^(l + ^ ^ g ^ 0) + yi ( i + tan ft sec 0) ~ - IT tan 2 0] . 



In this equation, /, as before, is written for the frequency of the elec- 

 trically maintained fork, and 1ST for the number of the teeth on the 

 apparently stationary circle. 



tt ■ * 2L/2L , 



U is written for — — _ _— 1 



The equation is correct if the torsion and deviation from level are 

 taken into account in the value of GK as has been explained. The 

 only approximation used in the equation is that of writing tan fx for 

 KM 

 GKH 



Results* 



The results of the calculation are collected in the following- table. 

 The first column contains the date on which the experiments were 

 made ; the second, the speed in terms of the number of teeth on the 

 stationary card ; the third column gives the deflection corrected for 

 all scale errors and variations of temperature during each set; the 

 fourth column shows the value of resistance in absolute measure as 



