Temperature. 



Conductivity 





1st specimen. 



o°c 



12-42 



50 



10'63 



100 



9-40 



JR. A. Daly — Abyssal Igneous Injection. 197 



Conductivity 

 2d specimen. 



9-21 



8-37 

 1-76 



150 8*68 7-38 



200 8-14 7'10 



Units in centimeter, minute and deg. Centigrade. 



Similarly, Weber measured the conductivity of gneiss at 0°C 

 and at 100°C and found the conductivity to be 578/416 greater 

 at the lower temperature than at the higher.* 



Barns proved that the thermometric conductivity of the 

 substance thymol increased 56 per cent in passing from the 

 liquid to the solid state at the same temperature (possible 

 through undercooling). f 



It is true that condensation through pressure increases the 

 conductivity for heat, but Arrhenius has pointed out that at 

 depths greater than only a small fraction of the earth's radius, 

 increment of pressure entails no corresponding increment of 

 condensation.^ This condition applies to the (gaseous) earth- 

 matter which, at the depth of several hundred miles, has 

 reached its co- volume. At this and at greater depths temper- 

 ature may be in complete control as regards the conductivity 

 for heat — an increase of temperature with still greater depth 

 involving a slow decrease of conductivity. 



These observations and conclusions indicate, first, that 

 experimental studies on the conductivity of rock-matter at dif- 

 ferent temperatures, in different states of compression, and in 

 the two states of aggregation (if such studies are possible), are 

 urgently needed ; secondly, that it is now impossible to calcu- 

 late the exact position of the level of no strain in the earth's 

 crust. Nevertheless, in an earth composed of a crust floating 

 on a substratum which, because it is fluid and hot, has a lower 

 thermometric conductivity than the solid, cool crust, we might 

 expect the level of no strain to be well within the crust even 

 if the initial temperature gradient were comparable to that 

 now observed in the earth's superficial shell. In a personal 

 letter to the writer, the Rev. Osmond Fisher states that, with 

 a liquid interior, there must be a level of no strain in the 

 crust ; and this is apparently true no matter what the initial 

 temperature may have been. He states, further, that u the 

 level of no strain would be the same whatever the conduc- 

 tivity ; but the time would not be the same. The position of 

 the level would not fall so rapidly if the conductivity was less." 



* R. Weber in Landolt and Bornstein's Phys. Chem. Tabellen. 

 + C. Barus, this Journal, vol. xliv, p. 15, 1892. 



£S. Arrhenius, Geol. Foren. Stockholm Forhandlingar, vol. xxii, pp. 

 396-7, 410, 1900. 



