72 PROCEEDINGS OF THE AMERICAN ACADEMY. 



the molten lava the temperature of the wall-rock would be about 

 1115° C.27 This estimate is based on the assumption that the dif- 

 fusivity for heat in rock at high temperature has the value given by 

 Kelvin. That value is certainly too high, but the temperature stated 

 for a point 12 meters from the contact would in any case be reached 

 after some centuries following the establishment of the lava column. 

 An idea of the heat loss by conduction may now be obtained. The 

 equation for heat flow is : 



q = kA- — -^-t, 



X 



where k is the coefficient of conductivity, A the area of the surface 

 traversed, a- the thickness of the plate traversed, t the time, T and Ti 

 the steady temperatures of the two sides of the plate. In this case we 

 may use C. G. S. units, with k 0.005 (certainly too high a value for 

 these temperatures), t one second, x 1200, and J. 2 7rr X 200,000. We 

 have 



q = .005 X 2 X 3.14+ X 10,000 X 200,000 X ^^^^~ |^^^ x 1 

 = approximately 4,450,000 gram calories. 



The result expresses the approximate amount of heat lost by con- 

 duction into the wall-rock during each second. 



Hate of Heat Loss through Radiation at the Crater. — Siegl has 

 recently supplied a datum required for estimating the heat lost by 

 radiation from the surface of the lava lake. The general equation is 



log >Sf = log c-f clog r, 



in which S represents the number of calories radiated per second, T is 

 the absolute temperature stated in degrees centigrade, and c and e are 

 constants. For basalt Siegl has found that c = (10)"^^ X 0.589, and 

 c z= 4.083.28 His experiments show that the equation holds for basalt 

 up to 472° absolute. It is very probable that it may be applied, with 

 relatively small, or at least non-significant, error, to basalt at the higher 

 temperatures and under the conditions of radiation represented at 

 Kilauea. Such extrapolation gives the following results : 



27 R. A. Daly, Amor. Jour. Science, 26, 23 (1908). 



*^ K. Siegl, Sitzungsber. Akad. Wissen. Wien, Math.-Naturw. Klasse, Bd. 

 116, 1203 (1907). 



