Potts — Rowland's New Method. 109 



consumption of energy will manifest itself by an apparent 

 increase in the resistance and consequently a greater ^ 2 E, loss. 

 This fact is made use of in the following method for the detec- 

 tion of short circuits in coils and was suggested by Professor 

 Bowland.* 



The method is as follows : the connections are as in fig. 2, 

 with the exception that a coil of wire is introduced in arm 1 in 

 place of the condenser. If the resistances are now balanced 

 until there is no deflection of the electro-dynamometer, and a 

 mass of metal approaches the coil, there will be a deflection of 

 the electro-dynamometer ; owing to the increase in the effective 

 resistance of the arm 1. If a coil of wire whose ends are not 

 connected be laid on top of the coil in arm 4 there will be no 

 deflection, while if the ends are connected or if there is a short 

 circuit in the coil there will be a deflection. 









Table 



XI. 











R 2 = 1010 



R 4 = 1507 





R 1 = 2257 



T=-015 





No. of 





Dia. of 





Uncorrected. 







turns. 





wire. 



R 3 





R'i 



D 



R c 









— 



6711 





226-8 









2" 



14 



1-59 



5882 





258-8 



9-15 cm. 



32-0 



3- 



22 



•62 



6497 





234-3 



2-21 



7-5 



5' 



25 



•44 



6520 





233-4 



1-90 



6-6 



Table XI shows the sensitiveness of the method. The coil 

 A of 5'3 henrys was used. The bridge was balanced and then 

 small coils of wire the same size as the inner diameter of the 

 coil were placed on the coil and the deflection noted ; and the 

 apparent increase of resistance was determined in the same 

 manner as the electric absorption in the case when the coil L 

 was replaced by a condenser. Column D gives the deflection 

 after the coils were placed on the large coil in arm 1 and R c is 

 the apparent increase in resistance of arm 1. It appears from 

 this table that with a coil of the size used, a short circuit in 

 another coil of same size could be detected, even though the 

 coil were of quite fine wire and only one turn was crossed. 

 Other conditions being the same, the sensitiveness varies 

 directly as the cross section of the wire in the coil to be tested, 

 if the resistance of the contact between the two ends of wire 

 is neglected. In cases where small coils are to be tested, the 

 sensitiveness may be increased by filling the center of the coil 

 with iron. And of course as short a period of current as avail- 

 able should be used. 



* This Journal, December, 1897. 



