476 



NATURE 



[July io, 1913 



of Education examination, and if the exercises are 

 performed under the supervision of a teacher, none 

 of its minor defects will cause the beginner to gain 

 wrong impressions. 

 Ministere de I' Agriculture. Direction Generate 



des Eaux ct Forets. 2 e partie. Eaux et 



Ameliorations Agricoles. Service des Grandes 



Forces hydrauliqu.es clans la Region des Alpes. 



Resultats des Etudes et Travaux a la Fin de 



191 1. Tome v., 1912. Pp. 530. 

 The present volume is the fifth of the series 

 published by the French Ministry of Agriculture 

 since the inauguration of the Service of the Great 

 Hydraulic Forces in Alpine regions, and it brings 

 the account of operations down to the end of 

 the year 191 1. Of the 530 pages of which the 

 volume consists, 487 are devoted to a tabulation 

 of the results obtained from observations in the 

 basins of the Arve, the Fier, the Isere, and the 

 Drome. A series of nine charts also accompanies 

 the report, covering the regions of the Arc, the 

 Breda, the Durance, and the Guil. 



It is interesting to note the expedients and 

 devices by which an investigation, demanding for 

 its most effective development the employment of 

 expert scientific observers, has been enabled to 

 be carried on to a large extent by voluntary 

 workers and local auxiliaries, for the most part 

 untrained and indifferently coordinated. Such 

 agencies in many cases have had to be relied upon 

 for the collection of data, and as there is a con- 

 stant change of personality in the assistants, the 

 difficulties in the way of securing trustworthy 

 records are sufficiently obvious. 



"However," concludes the prefatory note, "in 

 spite of defects, of which we more than anyone 

 are conscious, we are convinced that the study of 

 hydraulic forces, so far as circumstances permit, 

 constitutes none the less a real utility " — and a 

 cursory glance through the pages of statistical 

 matter, carefully annotated and compiled, bears in- 

 contestable witness to the patient labour and 

 exactitude of those engaged in the French hydro- 

 graphical service and of M. de la Brosse, its chief 

 engineer. 



Weather Bound. By R. T. Smith. Pp. 319. 



(Birmingham: Cornish Bros., Ltd., n.d.) 



Price 15s. net. 

 The author gives, in great detail, summaries of 

 results of twenty-seven years' observations at five 

 stations situated to the west of Birmingham, in a 

 series of tables and diagrams occupying- 170 pages. 

 He adds a diary, " Weatherwise and Otherwise," 

 for the same period, which occupies sixty pages, 

 and explanatory text (seventy-two pages). He 

 also gives a diagram of the normal course of 

 the meteorological elements throughout the vear, 

 which is unintelligible owing' to want of explana- 

 tion. The amount of industry displayed is worthy 

 of praise, and most of the tables appear to 

 •contain climatic data of real value, but the 

 author's exposition cannot be recommended to the 

 attention of serious students of meteorology. 



R. C. 

 NO. 2280, VOL. qil 



LETTERS TO THE EDITOR. 

 [The Editor does not hold himself responsible for 

 opinions expressed by his correspondents. Neither 

 can he undertake to return, or to correspond with 

 the writers of, rejected manuscripts intended for 

 this or any other part of Nature. No notice is 

 taken of anonymous communications.] 



Radio-activity and the Age of the Earth. 



In his letter in Nature of June 26, Dr. Schiller 

 quotes with disapproval Mr. Holmes's deduction that 

 the "heavy metallic core" of the earth "must be 

 completely destitute of radium"; for this deduction, 

 in Dr. Schiller's opinion, "involves the improbability 

 that the heaviest metal of all, uranium, has not gravi- 

 tated to the 'metallic core,' and does not explain 

 why this core should be destitute of radio-active 

 substances." 



In the next paragraph, however; Dr. Schiller sug- 

 gests a possible escape from the difficulty with the 

 words, " it is possible that under the physical condi- 

 tions obtaining in the interior uranium does not 

 dissociate, or does so much more slowly." 



Last autumn, as a sequel to certain speculations 

 into the effects of pressure on the mineralogical con- 

 stitution of the earth's crust at great depths, I was 

 led to a consideration of this very question of the 

 dissociation of elements when subjected to the high 

 temperatures and pressures that prevail at such depths. 



So far as I was able to discover, no determination 

 of the specific gravity of radium had then been made, 

 presumably for lack of sufficient material ; but, 

 judging from its chemical relationship with barium, 

 the atomic volume of radium must be much greater 

 than that of uranium. Heat is known to be evolved 

 during the disintegration of radium, so that the break- 

 up of this element is an exothermic change. I am 

 writing this letter whilst travelling, and am, conse- 

 quently, unable to verify my impression that heat is 

 also evolved during the conversion of uranium into 

 radium. But in any case, the passage of uranium 

 into radium may be expressed in a general way by 

 some such equation as the following : — 



U=Ra+»n+e J 

 where m indicates the loss of mass due to liberation 

 of helium in the successive stages of disintegration, 

 and e the loss of energy represented by the various 

 manifestations of energy. Since radium has a higher 

 atomic volume than uranium we see that the progress 

 of this reaction from left to right means an increase 

 in volume and an evolution of energy, part of which, 

 is doubtless speedily transformed into heat. In fact, 

 it is exactly the kind of reaction that would be in- 

 hibited by high pressure and temperature conditions. 



That high pressure should be able to prevent the 

 disintegration of uranium seems reasonable, if one 

 accepts the electronic constitution of the atom. Judg- 

 ing from the extreme length of the half period of 

 disintegration of uranium under surface conditions, 

 the constituent electrons of an atom of uranium per- 

 form on the average a vast number of revolutions 

 before the system arrives at the position of instability 

 that permits the escape of a helium atom. In fact, 

 the uranium atom is evidently stable during an 

 enormous number of revolutions or vibrations. And 

 if, when the electronic system arrives at last at an 

 unstable configuration, a sufficiently powerful counter- 

 balancing force can be applied from without, then the 

 system will be helped past the danger point and be 

 able to commence another long evele of movements 

 before the dangerous configuration is again assumed. 



In view of the experiments of Humphreys and 

 Mohler upon the displacement of the spectral 

 lines, and the work of Richards on the com- 



