124 Proceedings of Boyal Society of Edinhurgli. [ jan . 16 , 
the plates, no break being made in the circuit. The first reading 
was taken ten seconds after commencing the discharge. 
Deflection at intervals of five seconds. — 2*03, 1*43, 1*23, ITO, 1*02, 
0*93, 0*86, 0*81, 0*76, 0*71, 0*68, 0*64, 0*62, 0*59, 0*56, 
0*54, 0*52, 0*51, 0*49, 0*48, 0*46, 0*45, 0*44. 
At intervals of ten seconds. — 0*42, 0*40, 0*38, 0*37, 0*35, 0*34. 
At intervals of one quarter of a minute. — 0*32, 0*30, 0*29, 0*28, 0*27, 
0*25, 0*24, 0*24. 
At intervals of half a minute. — 0*22, 0*21, 0*20, 0*19. 
At intervals of one minute. — 0*16, 0*15, 0*13, 0*12, 0*12, 0*11. 
If we take the values of x for ^ = 10 and ^ = 20, and calculate 
from them the value of h in the equation 
/yi /y* C 
<A/ — J 
we get 5 = 0*05. This is the equation of the logarithmic curve 
which coincides with the observed curve when t is small. Hence 
b is approximately equal to the reciprocal of the product of the 
capacity and the resistance. Now, as already observed, the initial 
value of the transition-resistance when the charging current was 
started was about 600 ohms, and the final value was about double 
of this. Hence 
5 = 
1 
1200 C 
0*05. 
To obtain the value of the capacity in electrostatic units, we 
must convert the resistance in ohms into its equivalent in electro- 
static units. Thus gives 
C = J*10'\ 
The effective area of the two plates may be taken roughly as 
200 square centimetres. So the capacity per unit area is 
Hence the thickness of the dielectric is approximately 10~® cm. 
Sir W. Thomson’s higher and lower limits for molecular distances 
are 10“^ and J*10~® respectively. 
In conclusion, I have to acknowledge my indebtedness to Mr J. 
Butters for much valuable assistance, both in the experimental and 
numerical work. 
Added June 23. — The simpler empirical formula P’ix -a) — h may 
be used for purposes of calculation instead of (B) when t is not 
very large. 
