
592 Prof. J. A. Fleming on the Measurement 
TasLE ITI.—Results of Inductance Measurements on 
Short Coils, having a Dimension ratio of 7 : 1. 
(Telephone and buzzer in combination with Anderson’s method.) 



Mean 
AME Ue L. value L. 
ad ee m ohms: r. | . | Inductance and Calculated 
oil.) — nay e ohms. | mfds.| observed. greatest y 
= | Q R498 cms. deviation | formula. 
A 
B 
C 
D 
from mean. 

———— —_—————. +> —_____ 

10 | 1000 | 12-23 1223| 384+2 |-00272' 1,321,000 
34- 1,295,000 | 
72 ne 299 2 es! 
100} 110) 12-73 14) 1643-2222 | 1,288,000 | °1°56'000 | 1,379,800 | 


100] 100/13-00/ 13] 173 2222 | 1,288,000 | "73’9q9 
10 1000 12:22 1222| 370-+2 00272 1,282,000 | —}8 
100|1000|77:1 | 771) 1440+10 |-00272| 3,530,000 ee 3.918.200 
100) 100] 78-0 | 78| 51+<1 |2222 | 3594000; Tio | Sule 
10| 10/780 | 78) 96+ <1 |-2222 | 3,543,000 
100) 100} 83-0 83 49+1 |'2222 | 3,652,000 | +19,000 | 3,935,200 
100; 1000) 80:3 | 803) 1440-+5 |-00272 sg | soo 
10; 10) 83-0 83 941 |2222 | 3,652,000} —11,000 
| 

100; 100] 88:0 88 60+1 |:2222 | 4,302,000 ' +41,000 | 4,670,800 
10; 10) 38380 88| 10641 (2222 | 4,341,000 ) —43,000 


100} 1000| 76:9 | 769| 1450+4 |:00272) 3,550,000 


160 | 1000 | 86°5 | 865 1555-++5  |:00272 1308000 | 00 




of the long coil to be 20°6 millihenrys, and use the bridge 
readings to calculate the value of the capacity of the leyden- 
jars, we find it to be 0:00282 mfd. The values of this 
capacity measured by the intermittent discharge method was 
found to be 0°00272 mfd. Hence, the bridge-telephone- 
buzzer method, which needs no special appliances other than 
those found in every laboratory, provides a means of deter- 
mining with fair accuracy quite small capacities very easily, 
and can be applied to the measurement of the capacities of 
telegraph wires or aerials or very short lengths of cables. 
The method has been used for the calibration of a variable 
inductance made for certain resonance experiments. This 
inductance standard was constructed as follows :— 
A cylinder of boxwood about 10 centimetres in diameter 
and 45 cms. in length is provided at the ends with brass 
plates carrying centre pins, by means of which it is suspended 
in bearings. This cylinder is cut with a screw of 6 threads 
to the inch, and in this is wound a no. 14 8.w.G. copper wire, 
the ends of which are attached to the end plates. Parallel 
with the cylinder (see fig. 2) is fixed a brass rod about 1 cm. 
in diameter on which slides a travelling bar, the end of which 

=——— |——_--_-—__| 
