702 



SCIENCE 



[N. S. Vol. XXVIII. No. 725- 



grams (20,000 tons) of radium in its 

 waters. 



The experiments which I have been able 

 to make on deep-sea deposits, thanks main- 

 ly to the kind cooperation of Sir John 

 Murray, apply to ten different materials of 

 typical character. 



The results are so consistent as to lead 

 me to believe that although so few in num- 

 ber they can not be far wrong in their 

 general teaching. 



The means are : 



Extension : Mil- 

 lions of Square 

 Eadium Miles 



Globigerina ooze 7.2 49.5 



Radiolarian ooze 36.7 2.5 



Red clay 33.3 51.5 



Diatom oozes have not yet been examined. 

 It is apparent from these results that the 

 more slowly collecting sediments are those 

 of highest radio-activity, as if the organic 

 materials raining downwards from the sur- 

 face of the ocean carried everywhere to the 

 depths uranium and radium abstracted 

 from the waters ; but in those regions where 

 the conditions were inimical to the pres- 

 ervation 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 : 



The percentages of calcium carbonate are 

 from the report of the Challenger Expedi- 

 tion. The red clay in the table, which 

 reads as an apparent exception, is prob- 

 ably a ease of recent change in the char- 



acter 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 wiU remember many eases, 

 where recent change in the character of a 

 deposit is to be inferred. 



A point of much importance in con- 

 nection 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 evi- 

 dence that the full equivalent amount of 

 uranium is present is, I believe, conclusive. 



In the first place, to so vast a reservoir as 

 the ocean the rivers can not be supposed 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 necessarily 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 0.0042 X 10"^^ per cubic centi- 

 meter. That is less than the oceanie 

 amount. In short, it is evident that th& 

 uranium must accumulate year by year in 

 the oceanic reservoir, like other substances 

 brought in by the rivers, and that the pres- 

 ent state of the waters is the result of such 

 actions prolonged over geological time. 



While this reasoning is conclusive as re^ 

 gards the waters of the ocean, it does not 

 assure us that the sediments accumulating 

 in their depths are throughout as radio- 

 active as their surface parts would indicate. 

 There might be a precipitation of radium' 

 unattended by uranium, in which case 

 their deeper parts would not be radio- 

 active. 



Against this possibility there is the evi- 

 dence of such true deep-sea deposits as 

 were formed in past times and to-day still 

 preserve their radio-activity. For in- 

 stance, the chalk, which, considering that it 



