October 8. 1908J 



NA rURE 



595 



important. In the present paper the subject is considrrrd 

 from that point of view. 



There is soine difficulty in finding suitable material for 

 comparing the helium content of minerals with their geo- 

 logical age. The author has been fortunate in discovering 

 that phosphatic nodules (the so-called coprolites) and phos- 

 phatised bones are extremely rich in radio-active con- 

 stituents, sometimes containing fifty times as much radium 

 as the generality of rocks. These nodules and bones are 

 found in a great variety of strata, from the Pliocene down- 

 wards. The nodules frequently contain, or consist of, 

 fossils characteristic of the stratum to which they belong, 

 or of one very little earlier ; thus their age is well defined. 

 The same remark applies still more to the mineralised 

 bones. There is no reason to doubt that the radio-active 

 material was introduced into the bones by infiltration at 

 the time that they became phosphatised, and from that 

 epoch the accumulation of helium must be dated. 



In these e.Kperiments the author has extracted the helium 

 by solution of the powdered substance in liydrochloric acid. 

 The action takes place quite readily. 



Radium was determined by the methods described in 

 earlier papers. The solution obtained in extracting helium 

 was usually employed for the radium determination. 



The uranium oxide percentage was calculated from the 

 radium observations by standardisation with a uranium 

 mineral. 



The results mav be tabulated as follows : — 



his latest estimate. It is that 31b cubic mm. of helium 

 ire produced per gram of radium per annum. This is 

 deduced on the following assumptions : — 



(i) The number of helium atoms produced is equal to 

 the number of a particles emitted. 



(2) For every four o particles emitted by radium with 

 its immediate products, two are emitted by uranium, one 

 by ionium, and one by polonium. 



The author does not enter on any discussion of the 

 validitv of these suppositions, be\nnd remarking that there 

 are no definite grounds at present for deciding whethef or 

 ni't h( liu n is liberated in the rayluss changes. 



Taking the ratio of radium to uranium in minerals as 

 3-4x10-", we get for the annual iielium production ])er 

 gram of uranium oxide, (U,,0,) in a mineral, 9-13 X 10-' c.C. 



.■\dopting this rate of growth provisionally, the follow- 

 ing ages are obtained as a nilui}}iiti}i for some of the 

 materials examined : — 



Years 

 225,000 

 3,080,000 

 ,950,000 



Phosphatic nodules of the Crag 



Phosphatic nodules of the Upper Greensand.. 

 Phosphatic nodules of the Lower Greensand.. 

 Haematite overlying Carboniferous Limestone 141,000,000 

 It must be emphasised that these absolute values are 

 provisional only. It is hoped that geologists and others 

 will not regard the method as discredited if it should be 

 necessary to alter them considerably, when the rate o( 

 growth of helium has been directlv determined. 



It will be at once noticed that the order of stratigraphical 

 position is not accurately followed. For example, the 

 phosphatic nodules and bones from the Kimmeridge Clay 

 do not show so high a helium ratio as those from the 

 Lower or Upper Greensand, though they are geologically 

 older than either. At the same time it will be noticed 

 that helium ratios approaching 12, such as are common 

 in the mineral veins of Carboniferous age in Cornwall, 

 are not met with in the younger strata.' The facts arc 

 most easily explained by supposing that the retention of 

 helium has been often, if not always, imperfect. 



One point remains to be referred to. If thorium were 

 present in any of these materials we might expect it to 

 have a disturbing influence, as an independent source of 

 helium. The most searching experiments the author has 

 been able to make have only suggested a faint suspicion of 

 its presence in the phosphatic nodules and bones. It can 

 contribute nothing appreciable to their activity. The' same 

 applies to Cumberland haematite : in this case the results 

 were still more distinctly negative. 



The chief interest of the present results is in their 

 application to the measurement of geological time. For 

 this application we require to know the rate at which 

 helium is produced from i gram of uranium with the 

 equilibrium quantity of all the other products of the 

 series. 



Prof. Rutherford has kindly communicated to the author 



t Ex.imples will be found in Roy. Soc. Proc, A, vol. Ixxx.. p. 573. 

 The values are not reprinted here, as they were only obtained by the crude 

 method of heating the minerals. This, however, suffices to give the order 

 of magnitude. 



The conclusions of this paper may be summarised as 

 follows : — 



(i) Phosphatic nodules and phosphatised bones of_ all 

 geological ages possess marked radio-activity, many times^ 

 higher than that of rocks. This activity is due to pro- 

 ducts of the uranium series. 



(2) Helium has been detected in these materials, even 

 when they are not of more than Pliocene age. 



(3) The ratio of helium to uranium oxide has been 

 measured. This ratio does not strictly follow the order 

 of superposition of the strata ; but high ratios are not met 

 with in the vounger deposits, whereas they are common 

 in the older ones. It is conjectured that helium has been 

 imperfoctlv retained, at all events in some cases. 



(4) Provisional values are gi%'en for the time required 

 to accumulate the quantity of helium now found in the 

 nodules and other materials. 



Paris. 

 Academy of Sciences. Seplemb»r 7S.— M. Bourh.nrd in 

 the chair. — Two applications of Fredholin ',s equation to 

 some problems of niathematical physics : Emile Picard. 

 When a problem has been reduced to this equation it is 

 usually sufficient to examine whether this is a singular 

 case or not. In certain circumstances more complex con- 

 ditions inav arise ; two simple examples of such cases are 

 discussed in the present paper.— Experimental partheno- 

 genesis by electrical charges : Yves Delagre. The eggs 

 are placed in a vessel the base of which forms one plate 

 of an electrical condenser, and submitted to a series ^ of 

 charges. Blank experiments with the electrolytic solution- 



NO. 2032, VOL. 78] 



