KOTEMBEB 20, 190S] 



SCIENCm 



709 



far in excess of the radio-thermal heating. 

 From this state by a continual convergence, 

 the rate of radiation loss diminishing while 

 the radio-thermal output remained com- 

 paratively constant, the existing distribu- 

 tion of temperature near the surface has 

 been attained when the radio-thermal 

 supply may nearly or quite balance the loss 

 by radiation. The question of the possi- 

 bility of final and perfect equilibrium be- 

 tween the two seems to involve the interior 

 conductivity and in this way to evade 

 analysis. 



It will be asked if the facts of mountain 

 building and earth-shrinkage are rendered 

 less reconcilable by this interference of 

 uranium in the earth 's physical history. I 

 believe the answer will be in the negative. 

 True, the greatest development of crustal 

 wrinkling must have occurred in earlier 

 times. This must be so, in some degree, on 

 any hypothesis. The total shrinkage is, 

 however, not the less because delayed by 

 radio-thermal actions, and it is not hard to 

 point to factors which will attend the more 

 recent upraising of mountain chains tend- 

 ing to make them excel in magnitude those 

 arising from the stresses in an earlier and 

 thinner crust. 



UNDERGROUND TEMPERATURE 



It would be a matter of the highest in- 

 terest if we could definitely connect the rise 

 of temperature which is observed in deep 

 borings and tunnels with the radio-activity 

 of the rocks. We are confronted, however, 

 by the difficulty that our deepest borings 

 and tunnels are still too near the surface 

 to enable us to pronounce with certainty on 

 the influence of the radium met with in 

 the rocks. This will be understood when 

 it is remembered that a merely local in- 

 crease of radio-activity must have but little 

 effect upon the temperature unless the in- 

 crease was of a very high order indeed. 

 A clear understanding of this point shows 



us at once how improbable it is that vol- 

 canic temperatures can be brought within 

 a very few miles of the surface by local 

 radio-activity of the rocks. To account on 

 such principles for an elevation of tempera- 

 ture of, say 1,200° at a depth of three or 

 four miles from the surface, a richness in 

 radium must be assumed far transcending 

 anything yet met with in considerable rock 

 masses ; and as volcanic materials appear to 

 show nothing of such exceptional richness 

 in radium we can hardly suppose local 

 radio-activity of the upper crust respon- 

 sible for volcanic phenomena. 



When we come to apply calculation to 

 results on the radio-activity of the ma- 

 terials penetrated by tunnels and borings, 

 we at once find that we require to know the 

 extension downwards of the rocks we are 

 dealing with before we can be sure that 

 radium will account for the thermal phe- 

 nomena observed. At any level between 

 the surface and the base of a layer of 

 radio-active materials— suppose the level 

 considered is that of a tunnel— the temper- 

 ature depends, so far as it is due to local 

 radium, on the total depth of the rock-mass 

 having the observed radio-activity. This 

 is evident. It will be found that for ordi- 

 nary values of the radium content it is 

 requisite to suppose the rocks extending 

 downwards some few kilometers in order to 

 account for a few degrees in temperature 

 at the level under observation. There is, 

 of coui-se, every probability of such a down- 

 ward extension. Thus in the case of the 

 Simplon massif the downward continuance 

 of the gneissie rocks to some few kilometers 

 evokes no difficulties. The same may be 

 said of the granite of the Finsteraarhorn 

 massif and the gneisses of the St. Gothard 

 massif, materials both of which are pene- 

 trated by the St. Gothard tunnel, and 

 which appear to possess a considerable dif- 

 ference in radio-activity. In dealing with 

 this subject, comparison of the results ob- 



