136 ELECTRICAL MEASUREMENTS 



the above coils and by coils as ordinarily supplied by 

 tive American and German instrument makers. 



TABLE SHOWING INDUCTANCE EFFECTS IN RESISTANCE Con.s 



Micanite cards wound with resistance wire, such as are used for 

 series resistances in the potential circuits of alternating-current 



FIG. 61. Showing mounted resistance cards. 



instruments are highly satisfactory for general laboratory pur- 

 poses as they have considerable surface. Capacity effects should 

 be minimized by mounting the cards so that they are at least a 

 centimeter apart. The time constant of one of these cards is 

 10- 6 to 10- 7 second. Duddell and Mather's plan of weaving a 

 fine wire as the woof in a silk warp gives practically the same 

 results as the cards. 



