SELECTIVE ABSORPTION BY THE KARTlj's flU'ST, 185 



eventually to a solution of the puzzle. The various elements are 

 deposited from solution by the electric current with varying ease. 

 Thus, a given electro-motive force will deposit more iron and 

 magnesium than sodium or calcium ; as a matter of fact, calcium 

 ought to displace magnesium, and does so, under normal con- 

 ditions at the surface of the earth. The constant sinking of ions 

 of iron and magnesium carrying a positive charge towards the 

 centre of the earth may, in some way, cause the potential in the 

 lower regions of the crust to be such that the stronger elements 

 in the electro-motive seriesi such as sodium and lime, are repelled 

 to the surface, the weaker ones being also repelled, but the 

 centrifugal force, in their case, being counterbalanced by the 

 centripetal one due to the magnetic attraction of the earth's core. 

 If this be so, then, as all metallic ions carry positive charges, 

 directly metallic salts become dissolved by percolating water from 

 the rocks in which they are held, they would tend to seek the 

 surface, the stronger elements in the electro-motive series being 

 those most strongly repelled by the accumulated positive charge 

 at the base of the crust. The following is a short list of the 

 metals arranged in the electro-motive series, beginning with the 

 strongest, and it seems more than a coincidence that those metals 

 which are most widely distributed on the surface lie towards the 

 top of the series, whereas gold and platinum, which are scarce, 

 lie at the bottom of the series, as if their feeble electro-motive 

 force were insufficient to carry them in any quantity to the surface. 



Elcctro-uiotivc Scries of Elciiiciifs. 



Potassium {strongest). 



Sodium. 



Lithium. 



Calcium. 



Magnesium. 



Aluminium. 



Manganese. 



Chromium. 



Iron. 



Cobalt. 



Nickel. 



Hydrogen. 



Platinum. 



Gold (zveakcst). 



Uranium Ores. — Recent discoveries of uranium ores 

 are reported from tlie vicinity of Mount Painter, in the Flinders 

 Range, South Australia. This is of potential importance in view 

 of the close association of uranium with radium, and the com- 

 parative rarity of its ores in other parts of the world. Ores 

 containing niobium and monazite are also stated to occur in 

 the localitv referred to. 



