422 Scientific Intelligence. 
helped ourselves to attaining constancy of temperature in the 
stone by observing the current through the galvanometer, due to 
differences of temperature between any two of the three junc- 
tions B, M, T placed in circuit with it. 
(10.) We made many experiments to test what appliances might 
be necessary to secure against gain or loss of heat by the stone 
across its vertical faces, and found that kieselguhr, loosely packed 
round the columns and contained by a metal case surrounding 
them at a distance of 2 cm. or 3 cm., prevented any appreciable dis- 
turbance due to this cause. This allowed us to feel sure that the 
thermal flux lines through the stone were very approximately 
parallel straight lines on all sides of the central line BMT. 
(11.) The thermometer which we used was one of Cassella’s (No. 
64 ES with Kew certificate (No. 48,471) for temperature from 
0° to 100°, and for equality in volume of the divisions above 100°. 
We standardized it by comparison with the constant volume air 
thermometer* of Dr. Bottomley with the following result. This 
‘Is satisfactory as showing that when the zero error is corrected 
the greatest error of the mercury thermometer, which is at 211° 
C., is only 0°3°. 
Reading. Correction to be subtracted 
Air Mercury from reading of mercury 
thermometer. thermometer. thermometer. 
° ° 
0 1*9)- LO 
120°2 122°2 2°0 
166°8 168°6 1°8 
211°1 QV2°% 1°6 
265°7 267°5 1°8 
(12.) Each experiment on the slate and granite columns lasted 
about two hours from the first application of heat and cold; and 
we generally found that after the first hour we could keep the 
temperatures of the three junctions very nearly constant. Choos- 
ing a time of best constancy in our experiments on each of the 
two substances, slate and granite, we found the following results : 
Slate: flux lines parallel to cleavage. 
OCD) 50"2.-C, 
v(M)=123°°3. 
»(B) =202°°3. 
The distances between the junctions were BM = 2°57 cm. and MT 
=2°'6cm. Hence the formula of par. 2, 
K(M, B)_ 78°1+-2°6 — 28°1 
k(T, M) 79:02:57 30°7 
Aberdeen granite : 
= 0°98: 
u(t) = Bye 21 i 
v(M) =145°°6. 
v(B) =914°°6, 
* Phil, Mag., August, 1888, and Edinb. Roy. Soc. Proc., January 6, 1888. 
