of Small Inductances and Capacities. 089 
the number of turns per centimetre of length of the spiral 
was 24°96. 
This long coil belonged to a resonance apparatus designed 
by Seibt, and is hence alluded to as the long Seibt ‘coil. 
The resistance of the wire on this coil was about 152 ohms, 
and it was connected to a Wheatstone’s bridge (as shown in 
fig. 1), the other arms of which are denoted by P, Q, and 8. 
“The arrangement of apparatus used, consisted therefore 
of an ordinary y Post-Office plug W heatstone’s bridge having 
the spiral of which the inductance was to be determined 
connected to it. The battery-circuit contained the buzzer, 
and the bridge-circuit a telephone in series with a plug 
resistance-box, affording values for 7. The condenser con- 
sisted of one or more leyden-jars or a mica condenser. The 
steady balance was obtained first in the usual way with a 
galvanometer and steady current. 
The following Table gives the values of the bridge-arms, 
the bridge resistance 7, the capacity used, and the inductance 
L caleulated from the formula given by Anderson. 
The Table contains two sets of measurements, one set 
marked A, made by Mr. Shields with the Fleming-Clinton 
commutator, and the other marked B, made with the 
telephone and buzzer as above described. 
TaBLE I.—Results of Inductance Measurements of a 
Long Coil, having a Dimension ratio of 50:1. 





| | ; 0. L. 
) P. Q. R. 8. a in mfds. | observed in ems. 
100 1000 | 152-26 | 1522-6 | 4260 0.00272 | 19,900,000) 4 
100 1000 | 15231 | 15281 | 7675 0:00149 | (sone 
100 1000 | 15171 | 1511 4400+50 | 0:00272| 20,300,000 \ 
1000 | 10,000 | 151-3 | 1515 3350 £50 | 0:00272! 19,200,000 | 
100 10,000 | 151°5 | 15150 365+5 | 000272) 19,300,000 
1000 1000 | 152 152 24200+100 | 0-:00272 | 20,100,000 
100, 1000 | 151-4 | 1514 4400+50 | 0:00272 20,300,000 + B 
1000 10,000 | 1514 | 1514 3330+20 | 0:00272! 19,200,000 
10! 1000 | 151-7 | 15170 485+5 | 000272! 20,600,000 
100 10,000 | 151-7 | 15170 | .865+5 | 0:00272) 19,300,000 | 
100 | 100 | 152 | 152 217+1 | 0-256 | 20,800,000) 



Mean of A readings=19°7 x 10° ems. 
Mean of B readings=19°9 x 10° cms. 
Value calculated from the formula L=(zD¢)(7DN)=20'6 x 10° ems. 
By numerous observations on coils of this kind, sometimes 
50 diameters long or even less, the wire being wound ina 
single layer and in closely adjacent turns, the writer has 
