718 Dr. Stroud and Mr. Gates on the Application of 



Table VI. 





Capacity, 



r. 



L. 





•05 B 



33078 



•44355 henries 



S = 985-2 ohms. 



•05 A 



33648 



•44354 „ 



Q- 984-7 ohms and 



•05B + ^05A 



1056:} 



•44275 „ 



P = 130 ohms. 



•2B 



8066 



•44146 ,. 



All values of resist- 



•2 A 



8091 



-44113 ., 



ances are given in 



•2A-f05A + -05B 



52090 



-44116 „ 



legal ohms. 



•2B-f05A+05B 



51970 



•44118 „ 



The capacity used 



•2A-f--2B 



3788-5 



•44101 ., 



i vras the Elliott box 



•6 



2911-8 



44266 :, 



i and the names of 



•2A+^2B + ^05A-f05B 



29300 



•44137 „ 



the various plugs 



•5 + ^05A-f-05B 



•23370 



•44146 ., 



; are used to denote 



•5 + -2A 



1941^1 



•44157 ,. 



the capacities. 



•5-f-2B 



1938-6 



-44154 „ 



; 



•5+-2A+05A+-05B 



1635-9 



•44152 ,. 





•O4--2B + -05A4--05B 



1634^1 



•44149 ,. 





•5 + -2A+-2B 



] 400-6 



•44125 „ 



I 



•5+-2A-f-2B+05A+-05B 



1211-2 



-44139 ., , 



1 



We therefore decided to see what could be done in the way 

 of measuring a ver}^ small inductance indeed. We took a 

 coil of copper wire, having 4 layers of 80 turns each, the 

 resistance being 0*2 ohm. The length of the coil was 

 16'6 cms. and the mean diameter 2*1 cms. We can roughly 

 calculate a superior value for the inductance of this, by 

 assuming the field uniform and neglecting the effect of the 

 ends. We have L = 47rN^A//, where N represents the total 

 number of turns, I the length of the coil, and A the equi- 

 valent area. N and ^ could be accurately obtained, but A 

 may easily have been +10 per cent, wrong. Substituting in 

 the above formula we obtain L%268 microhenries. 



This inductance was measured as described above, but with 

 this modification, which is, we think, an improvement when 

 the greatest possible accuracy is desired. A balance was 

 obtained with stead}- currents on a sensitive bridge by varying 

 a high resistance S used as a shunt to the coil C. A piece of 

 copper wire W of the same cross-section as C and of slightly 

 longer length was taken, and by means of a rock- over switch 

 could be readily substituted for C The length of W, about 

 30 feet, was then carefully adjusted until it produced precisely 

 the same (almost zero) effect as C itself. This length was 

 then (while still connected to the switch) wound non-induc- 

 tively and then placed in contact with the coil. The shunt S 

 was now removed and the rock-over switch together with C 

 and W were transferred to the inductance-bridge and placed 



