390 
PROFESSOR C. H. LEES: THERMAL AND ELECTRICAL 
x A = a i + b', where a x — distance from enclosure to near 
edge of first sleeve. 
x B — x A +2b' + a 2 = a 1 + a 2 +Sb', where a 2 = distance between the near edges 
of first and second sleeves. 
x c = x B + b' + a 3 = a x + a 2 +a 3 + 4b', where a 3 = distance between the near edges 
of second and third sleeves. 
x c , = x c + ^b' = a 1 + a 2 +a 3 +4'7b'. 
rtj and a 3 were in every case made 0'10 centim. 
Estimation of the Small Difference of Temperature between the Rod and the 
Platinum Resistance Coils. 
In addition to a slight difference between the temperature v 0 of the rod and 
that of the sleeve, v' 0 , at the central transverse section of the sleeve, there is 
a further slight difference between the latter and that of the wire of the platinum 
resistance v" 0 , which may both be calculated with sufficient accuracy for the present 
purpose by taking 
pk 
% ,; o_ p'P" V 0 V 0 
ft ^0 
V 
t 
/// 
: fhv' 
0 ) 
where p= 1*84 centims. is the perimeter, t" — 0'0012 centim. the thickness, k" — 0'0004 
the conductivity, of the layer of oil between the rod and sleeve, p' = 2*14 centims. 
the perimeter, t"' = 0'014 centim. the mean thickness, # k"' — 0*0006 the conductivity, 
of the layer of silk and shellac between sleeve and wire, and p" = 2*28 centims. the 
perimeter of the outer surface of the wire. 
From the above we obtain 
v 0 = (1 + 29 h)v" 0 . 
Within the range of temperature covered by the experiments Ovaries from 0*00016 
at 110° absolute to 0*00027 at 300° absolute. Taking the mean value 0*00022 as 
sufficient for the present purpose, we find 
v 0 = l-006v" 0 ..(11) 
In the work which follows, the mean temperature of the platinum coil wound on 
the sleeve so as to cover 0*4 centim. of its length is taken as identical with the 
temperature at the centre of its length, the difference between the two being too 
small to influence the results appreciably. 
* Obtained from the minimum thickness, 0 - 012 centim., by the addition of a correction suggested by 
Maxwell’s ‘ Electricity and Magnetism,’ I., p. 280. The thermal conductivities are only known roughly, 
so that the final value of the correcting term is not likely to be very accurate. Its influence on the values 
of the conductivities is, however, very small. 
