PRESIDENTIAL ADDRESS. 



681 



The Ocmn and its Sediments. — The waters of the ocean, coveriug five-sevenths 

 of the earth's surface to a mean depth of 3'8 kilometres, represent the most 

 abundant surface material open to our investigation. As the mean of a very large 

 number of experiments upon twenty-two different samples of sea-water from 

 various widely separated parts of the ocean, I obtain a mean of 0016 x 10"^'^ gram 

 per cubic centimetre. There is considerable variability. Taking the mass of the 

 ocean as 1"458 x 10'* tonnes, there must be about 20 x 10^ grams (20,000 tons) of 

 radium in its waters. 



The experiments which I have been able to make on deep-sea deposits, thanks 

 mainly to the kind co-operation of Sir Johsi Murray, apply to ten different materials 

 of typical character. 



The results are so consistent us to lead me to 

 number they cannot be far wrong in their genen. 



The means are : — 



believe that although so few in 

 teaching. 



Globigerina Oozo 

 Kadiolarian Ooze 

 Red Clay . 



Raclium 



7-2 



a6-7 

 33-:] 



Exteusiou : Millions of 

 Square Miles. 

 19-5 



2-r, 



Diatom Oozes have not yet been examined. 



It is apparent from these results that the more slowly collecting sediments arc 

 those of highest radio-activity, as if the organic materials raining downwards 

 from the surface of the ocean carried eveiywhere to the depths uranium and 

 radium abstracted from the waters ; but in those regions where the conditions 

 were inimical to the preservation of the associated calcareous tests, there was the 

 less dilution of the radio-active substances accumulating beneath. The next table 

 shows that radio-activity and the percentage of calcareous matter in these deposits 

 stand in an inverse relation : 



Calcium Carbonate 

 per cent. 



92-21 

 (5i34 

 12-00 

 28-28 

 10-19 

 3-89 



I 



Kadium 



6-7 

 7-4 

 154 

 52-6 

 22-8 

 50-3 



The percentages of calcium carbonate are from the Report of the 'Challenger' 

 Expedition. The I\ed Clay in the table, which reads as an apparent exception, is 

 probably a case of recent change in the character of the deposit, for the evidence 

 of manganese nodules and sharks' teeth brought up with this clay is conclusive as 

 to the slow rate of its collection. Readers of Sir John Murray's and Professor 

 Renard's report will remember many cases where recent change in the character 

 of a deposit is to be inferred. 



A point of much importance in connection with our views on oceanic radio- 

 activity is that of the presence in the waters and in the deposits of the parent 

 radio-active substance, uranium. The evidence that the full equivalent amoimt 

 of uranium is present is, I believe, conclusive. 



In the first place, to so vast a reservoir as the ocean the rivers cannot be sup- 

 posed to supply the radium sufficiently fast to make good the decay. In a very 

 few thousand years, in the absence of uranium, the rivers must neceesari'y renew 

 almost the entire amount of radium present. I have made examination of the 

 water of one great river only — the Nile. The quantity of radium detected 

 was 00042 x 10'- per cubic centimetre. That is less than the oceanic amount. 

 In short, it is evident that the uranium must accumulate year by year in the oceanic 

 reservoir, like other substances brought in by the rivers, and that the present state 

 of the waters is the result of such actions prolonged over geological timf>, 



