312 HENKY A. EOWLAND 



This is a very good method in many respects. 



For using 25 and 26, a key to make instantaneous change of connec- 

 tions is almost necessary. 



To measure resistance by alternating currents, a Wheatstone bridge 

 is often used with a telephone. 



I propose to increase the sensitiveness of the method by using my 

 method of passing a strong current through the fixed coils of an 

 electrodynamometer while the weaker testing current goes through the 

 suspended system. 



Using non-inductive resistances, methods 10, 13 A, B, C, and 14 all 

 reduce to proper ones. 10 or 14 is specially good and I have no doubt 

 will be of great value for liquid resistances. The liquid resistances 

 must, however, be properly designed to avoid polarization errors. The 

 increase of accuracy over using the electrodynamometer in the usual 

 manner is of the order of magnitude of 1000 times. 



Since writing the above I have tried some of the methods, especially 

 6 and 12, with much satisfaction. By the method 12, results to 1 in 

 1000 can be obtained. Eeplacing U by an equal coil, the ratio of the 

 two, all other errors being eliminated, can be obtained to 1 in 10,000, 

 or even more accurately. 



The main error to be guarded against in method 12, or any other 

 where large inductances or resistances are included, arises from twist- 

 ing the wires leading to these. The electrostatic action of the leads, 

 or the twisted wire coils of an ordinary resistance box, may cause errors 

 of several per cent. Using short small wire leads far apart, the error 

 becomes very small. 



Method 6 is also very accurate, but the electric absorption of the 

 condensers makes much accuracy impossible unless a series of experi- 

 ments is made to determine the apparent resistance due to this cause. 



In method 12 I have not yet detected any error due to twisting the 

 wires of coils I. However, the electrostatic action of twisted wire coils 

 is immense and the warning against their use which I have given above 

 has been well substantiated by experiment. Only in case of low resist- 

 ances and low inductances or in cases like that just mentioned is it to 

 be tolerated for a moment. Connecting two twisted wires in a coil in 

 series with a resistance between them, I have almost neutralized the 

 self induction, which was one henry for each coil or four henrys for 

 them in series;! 



Altogether the results of experiment justify me in claiming that 



