WATEE AND VOLCANIC ACTIVITY DAY AND SHEPHERD. 305 



Daubree's experiment is the surface tension of water only/ and water 

 will obviously have no surface tension above its critical temperature 

 of 374° (except perhaps in so far as salts in solution may have the 

 effect of raising this critical temperature slightly). This tempera- 

 ture passed, water must make its way precisely like any other gas 

 by diffusion through pores or by overcoming whatever chemical or 

 mechanical conditions it may encounter. The prospect is not an 

 encouraging one. The hydrostatic pressure at great depths of the 

 sea would appear to be the only sufficiently powerful agent to drive 

 water against a high adverse temperature gradient, but to invoke 

 this would be to invite nice distinctions of where " magmatic " water 

 begins and "meteoric" water ends. The presence or absence of 

 chlorine is not a conclusive factor one way or the other, because the 

 physical processes of infiltration through porous rock and of distil- 

 lation are alike of such a land as gradually to leave the dissolved 

 salts behind ; this is illustrated by the fact that the bore holes yield 

 fresh water except when the infiltration is very rapid. 



To us, therefore, such evidence as there is appears to indicate that 

 the water released from the liquid lava when it reaches the surface 

 is entitled to be considered an original component of the lava with 

 as much right as the sulphur or the carbon. 



1 " Capillary forces are effective only when there is a surface of separation within the 

 pores. * * * Since the pressure discontinuity occurs only at the surface of separa- 

 tion, a column of liquid can be supported only when there is a free liquid surface within 

 the capillary. * * * 



" * * * As regards the influence of temperature on the surface tension of water, all 

 the investigations unite in showing that Its surface tension decreases regularly with rise 

 of temperature, becoming zero, of course, at the critical temperature where there is no 

 surface of separation. The relation is practically linear when the whole range is con- 

 sidered : it may be represented with sufficient accuracy by the formula. 



f <=T8-0.21 t or 0.21 (370-t) 



where c t I« the surface tension at t° (temperature centigrade) expressed in dynes per 

 centimeter. 



" * * * From this * * * it is evident that the pressure producible by capil- 

 larity is Insignificant in comparison with the hydrostatic pressure, except for very fine 

 pores * * * and this minuteness of the pores leads us to inquire what amount of 

 water could actually flow through them. * * * Assuming the mean viscosity of tho 

 water to be 0.005 (its value at a temperature of 30°), the amount of water flowing 

 through a pore of diameter 1 p. (i. e., 1/25,000 inch) would be about 15 x lO-a cc. per 

 year. * * * Now, if we make the very generous estimate that 10 per cent of the 

 volume occupied by the rock consists of pore spaces * « * t^g quantity of water 

 flowing would be only 15 cc. per sq. cm. of surface per year. « * * jf |-jjg diameter 

 of the pores is 0.01 n the amount of water flowing would be 0.0015 cc. per sq. cm. of 

 surface per year. * * * in other words, a period of 1,000 years would be required 

 for a quantity of water equivalent to 1.5 cms. (about one-half inch) of rain to flow past a 

 given horizontal plane. 



" * * * It appears, therefore, as if the probabilities were all against the notion 

 that appreciable amounts of meteoric water can ever penetrate into deep-seated and 

 highly heated rock masses." (John Johnston and L. H. Adams : " Observations on the 

 Daubrge experiment and capillarity in relation to certain geologic speculations." Journal 

 of Geology, vol. 22, in press, 1913.) 



44863°— SM 1913 20 



