372 Proceedings of the Royal Society of Edinburgh. [Sess. 
The resistance of the resonator was about 0*54 ohms, a m was 88 cms., 
and the diameter of the rods 5 mm. Its self -inductance, therefore, when in 
resonance with the oscillator was 730 cms. y 2 was thus found to be 0*015. 
7i + 72 was determined experimentally, y 2 subtracted, and the values of y v 
the logarithmic decrement of the vibrations in the oscillator, determined for 
different materials of the electrodes and various lengths of spark gap. 
Variation of Logarithmic Decrement y l with Metal, 
and Length of Spark Gap. 
Zinc — 
Gap . 
Decrement 
Aluminium — 
Gap . 
Decrement 
Cadmium — 
Gap . 
Decrement 
Tin— 
Gap . 
^ Decrement 
Copper — 
Gap . 
Decrement 
Iron — 
Gap . 
Decrement 
Brass — 
Gap . 
Decrement 
Nickel — 
Gap . 
Decrement 
0*4 
0-85 
0*32 
0*24 
0-4 
0-8 
1*08? 
0*53 
0*45 
0-8 
0-26 
0-25 
045 
0-8 
0*45 
0-41 
0*4 
07 
0-30 
023 
0-45 
0*75 
0-33 
0-25 
0*35 
0*8 
0*20 
019 
0*45 
0-8 
0*39 
0*28 
IT 
1-4 
0-27 
0-23 
1*05 
1*5 
0*44 
0-27 
IT 
1*6 
0*22 
0*18 
IT 
1-5 
0-40 
0-25? 
IT 
1*5 
0*24 
0*29 
IT 
D45 
0*30 
019 
IT mm. 
0-20 
1T5 
1-45 
0-26 
0-23 
1*8 2*2 mm. 
0-24 0*29 
2-0 mm. 
0-24 
2*4 mm. 
0-22 
2 '4 mm. 
0*28 
1*9 mm. 
0*21 
1*7 mm. 
0-31 
1*7 mm. 
0-21 
The resistance of the spark gap in ohms can be obtained approximately 
by multiplying the above values of y 1 by 23. The smallest resistance 
recorded is therefore about 5 ohms. The period of the oscillator was 
4 10 -8 seconds. 
As will be seen from the table, the values of the decrements for different 
spark gaps do not agree well. The resistance of the spark gap itself seems 
to vary irregularly, and I could not get a steady deflection of the galvano- 
meter. Four induction coils were tried, also different breaks; the ordinary 
hammer break, the Wehnelt electrolytic break, and the Foucault mercury 
break were used. The break giving the most regular results was one 
driven by a motor, and consisting of a platinum strip pressing against the 
rim of a brass wheel, in which pieces of slate had been set. All the values 
