594 Measurement of Small Inductances and Capacities. 
the instrument has been divided to read in microhenrys 
directly. 



TABLE IV. 
{ 
No. of turns | Inductance | No. of turns | Inductance 
of wire. in cms. of wire. in ems, 
0 A 60 124,000 
10 10,000 70 148,000 | 
20 28,000 80 172,000 
30 50,000 90 196,000 | 
40 75,000 100 220,000 
50 100,000 Total | 227,000 





The above observations have been set out in a curve (see 
=) 
Fig. 3. 

NUMBER OF TURNS 

SELF {INDUCTION iN MICROHENRYS 
Such a graduated standard of inductance is useful in tuning 
wireless telegraph-circuits and in experiments on resonance. 
By the above described method the measurement of in- 
ductances, even as small as 2 or 3 microhenrys, is reduced to 
an extremely simple straightforward method, capable of being 
carried out without any special appliances, other than those 
found in every testing-room and laboratory. By its aid 
inductance as small as 10 microhenr ys can be measured with 
an accuracy of about 5 per cent., and inductances of the order 
of a millihenry with an accuracy of at least 1 per cent. 
A good method of constructing a small inductance of 
known value is to stretch two round wires of diameter d ems. 
parallel to each other at a distance D cms. apart. If these 
are short-circuited at the far end by a cross bar, first at one 
