AND ITS INHABITANTS 31 



revolution compared to those of Mars and the outer planets 

 suggests that the tidal forces of the moon and sun have pro- 

 duced a notable slowing down of the earth also. The largest 

 planet, Jupiter, 86,500 miles in diameter, revolves the most 

 rapidly, completing one revolution in 9 hours 55 minutes; 

 Saturn, the next largest, revolves in 10 hours 14 minutes. 

 Uranus also shows by the pronounced polar flattening of its 

 disc that it revolves in some similar short period. Mars, with 

 a diameter approximately half of that of the earth and a 

 twentieth of that of Jupiter, revolves in 24 hours 37 minutes. 

 These planets can never have suffered largely from tidal 

 retardation and a rough rule appears to prevail that the larger 

 the planet the more rapidly it rotates. Judging from its mass, 

 the earth may consequently have originally rotated in a period 

 of between 15 and 20 hours. This argument is only of sug- 

 gestive value, but it is in accord with other lines of argument. 

 If the moon passed through a viscous state sufficiently pro- 

 longed for it to respond completely to tidal control in its 

 rotation period, the presumption is clearly that the earth, a 

 larger body and better able to retain its heat, also passed 

 through a similar stage of viscosity. The present rigid and 

 elastic condition of the earth appears then to be a secondary 

 feature and the present ineffectiveness of the tides cannot be 

 safely used as an argument against the strong indications of a 

 primordial tidal retardation. ^/ 



Significance of the oceanic salt. Sodium derived from the 

 weathering of igneous rocks has been stored through all geo- 

 logical time in the ocean as sodium chloride. The ocean has 

 grown more salty since it first gathered on the earth, yet it is 

 so far undersaturated that sea water must be nine-tenths 

 evaporated before sodium chloride begins to be precipitated. 

 Furthermore, the indications are that it never was saturated, 

 even though in primordial times the sea water ma^ have been 

 less in volume. Concentration to a degree which eliminates 



