136 



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



succeeding nights it was found that the curve could not be sufficiently- 

 well determined by the observations, and that the assumption of a 

 uniform rise in resistance during the time elapsing between two suc- 

 cessive measurements would give as good results as the experiments 

 themselves would allow us to obtain. The proper determination of 

 this correction is a subject to which we shall have to give some atten- 

 tion in the more accurate measurements which we have in view. At 

 present it will suffice to point out that, as far as we can judge, the 

 error due to uncertainty of temperature is not more than "05 percent, 

 during the first set of spinnings on each night. It is much smaller 

 in the succeeding sets. It may increase the clearness of this account 

 if at this point we give a specimen, worked out in detail, of one set of 

 deflections. Let the resistance of our standard German silver coil, 

 which we always have assumed to be at the temperature of the air, 

 be called S, and the resistance of the rotating coil C. A comparison 

 by means of the balance shows that 



C=S + a, 



where a is the resistance of a certain length of the bridge wire, dif- 

 fering slightly at the beginning and end of the experiment. 



December 6. 



Number of teeth on stationary circle, 32. 



Comparison of resistance, C = S + *0225. Time = 9 h 17 m . 



Position of rest 766-43. Time = 9 h 32 m . 



Auxiliary magnetometer .... 26*9. 



Times 9 h 37 m . . 9 h 42 m . . 9 h 47 m . . 9 h 5o m 



t= 13°-0 .. 13°-0 .. 13°-0 .. 13°-0 



Hotation negative. . positive . . negative. . positive 



Deflected reading 367*60 .. 1166 40 .. 366*23 .. 1166*09 



Auxiliary magnetometer . . 27-55 .. 28"24 .. 28*50 .. 28*30 



Auxiliary magnetometer .... 27'2. Time= 9 h 57 m . 



Position of rest 767*08. 



Comparison of resistance, C = S + '0272. Time = 10 h m . 



From the comparison of zeros with the auxiliary magnetometer at 

 the beginning and end of the experiments, we find for the correspond- 

 ing readings during the experiments, 766'78 and 27*05. Con- 

 sidering that increased readings, if the magnet in the coil corre- 

 spond to decreased readings in the auxiliary magnetometer, we find 



