85 263 



When one considers that Iho supply of the emanation is llius evolved from 

 rocks ranging over a large area, one can readily understand that the amount of 

 emanation contained in the spring gases is not dependent solely on the amount of 

 radium contained in the rocks, but also on the facility with which these rocks 

 give off the emanation. As already mentioned, the decay of the emanation will 

 also tend to increase the uncertainty of deducing from the emanation contained 

 in the spring gases the amount of radium in the rocks, for it is difficult to say 

 how much time has elapsed since the gases were in contact with the rocks pro- 

 ducing the emanation. 



A peculiarity of the hot springs is that they are generally found gathered in 

 groups, being of course confined to fissures in the crust of the earth, (see p. 68). 

 The reason for this is, that it is only where fissures are found in the crust that 

 water can penetrate sufficiently deep down into the earth to become hot. In my 

 opinion, one has no ground for expecting to find any special agents which produce 

 the heat necessary for the thermal activity of the springs, inasmuch as this activity 

 is undoubtedly occasioned by the fact that the heat present in the interior of the 

 earth can be transmitted without difficulty to the earth's surface at the places 

 where the hot springs are situated. 



But the transmission of heat from the interior of the earth takes place al- 

 most exclusively by means of convection of hot water and steam through fissures 

 in the crust of the earth. 



It will readily be seen that, at the places where the thermal springs are, the 

 earth must suffer an extraordinary loss of heat. An estimate of this loss of heat 

 can be obtained by means of a simple calculation. The temperature gradient of 

 the earth is generally estimated at Ü.000304" per cm., and the earth's coefficient of 

 heat conductivity at 0.0041. Hence we get the loss of heat through each square 

 cm. of the earth's surface per second as 0.0000125 gram calories, or through a 

 square km. 12500 gram calories. It is sufficiently accurate to reckon the mean 

 temperature of Iceland at 0" C, and assuming that the thermal activity of the 

 springs will raise the temperature of 1 litre of water to 100° C. in one second, the 

 heat consumption amounts to 100000 gram calories, which, according to the 

 above calculation, corresponds to the loss of heat from 8 square km. of the earth's 

 surface. But in reality the loss of heat from the spring groups explored by us is 

 undoubtedly much greater. For these spring groups deliver on an average more 

 than 1 litre of water at 100" C. per second, and the spring water has already lost 

 a great deal of its heat energy on its way up to the earth's surface, partly from 

 heat conduction from the spring channel to the surroundings, and partly on ac- 

 count of evaporation. I presume therefore that the loss of heat on the part of the 

 earth through the thermal activity of the springs is not exaggerated when we 

 reckon it, at each of the spring groups we investigated, at from 5 to 10 times as 

 great as calculated above, or as great as the loss of heat due to conduction from 

 about 60 square km. of the earth's surface. 



