348 MODERN' METHODS OF WATER PURIFICATION. 



I conclude these remaiks with a quotation referring to 

 chemical treatment of turbidity from Hazen's book: — 



" Without such treatment no amount of filtration — single, double, or 

 multiple — will remove it. With such chemical treatment adequately 

 carried out, the simplest and easiest filtiation will suffice to make the 

 most refractory water as clean as distilled water." 



INTERNAL STRUCTURE OF THE EARTH.— In 



the Wilde lecture, delivered by Sir Thomas Holland, F.R.S., 

 in Manchester, on the 22nd March, the' lecturer remarked that, 

 except for geological observations, which rarely penetrated 

 deeper than one two-hundredth part of the earth's radius, we 

 were dependent upon mathematicians for our ideas respecting 

 tlie physical condition of the interior of our planet. Laplace's 

 hypothesis, he fm^ther said, is being largely superseded by 

 Chamberlin's planetesimal theory. Astronomers gave the 

 preference to the view of a solid globe, but not on the grounds 

 accepted by Kelvin. Arrhenius was of opinion that the core 

 of the earth was a dense gas. 



Differences of view were also being manifested regarding 

 the temperature of this inner core. Until recently the generally 

 received opinion was in favour of a hot interior, but Prof. 

 Schwarz, of Grahamstown, inclines to the view of internal cold. 

 The actuarial value of the earth's natural life is much increased 

 by the discoveries of embarrassingly large quantities of radium, 

 so that, instead of the termination of all life by intense cold. 

 Prof. Joly thinks that catastrophic heating may bring about 

 the final stage. 



The seismographic records for long distances. Sir Thomas 

 went on to say, due to earthquake waves passing along chords 

 drawn from one point on the earth's surface to another, show 

 that velocity is reduced when the distance traversed is long 

 enough to pass through the inner two-fifths of the earth's core, 

 and it is suggested that the central core therefore differs in 

 character from the outer three-fifths and from the surface 

 crust. 



