466 



NA TURE 



[September io, 1908 



APPENDIX A. 



Convecthe Movement of Uraiiiuin to the Earth's Surface. 

 — The estimate of temperature given assumes (i) that 

 the mass of igneous material is spherical, and (2) that 

 its surface is kept at constant temperature, heat escaping 

 freely. The first assumption is in favour of increasing 

 the estimate of te.nperature, and probably would not 

 generally be true, especially of a mass moving upwards. 

 The second assumption tends to give a lower estimate of 

 temperature, and is certainly misleading, as the surround- 

 ing materials are non-conducting, and must favour the 

 accumulation of radio-active heat. 



On assumptions (i) and (2) and on Barus' results for 

 the thermal expansion of diabase between 1100° and 

 1500°,' and results of my own on basalt," which are in 

 appro.\imate agreement, and assuming the mean excess of 

 temperature to be 500° and the surrounding materia! to 

 be at a fluid temperature, the force of buoyancy comes out 

 at more than 60 dynes per cubic centimetre of the 

 spherical mass. This is an under-estimate. 



If we may assume that the Deccan Trap is indeed an 

 instance of such an over-heated mass escaping at the 

 surface, and that similar radio-active masses rising up 

 from beneath at various times in the past may have 

 affected the crust, we have at our disposal a local source 

 of energy of plutonic origin which may account for much. 



APPENDIX B. 



Sedimentation and Rise of Geothcrms. — The depth of 

 the upper radio-active layer is, of course, unknown. 

 We possess, however, the means of arriving at some 

 idea of what it must be. The quantitative thermal 

 conditions impose a major limit to its average thickness, 

 and tile indications of injected rocks suggest a minor 

 limit. 



It will be found that if 2-6xio-° calorics is the heat 

 output of the whole earth per annum, and if we assign 

 only one-fifth of this amount to cooling due to decay of 

 the uranium, then, on the assumption that the earth is 

 no longer losing any part of its original store of heat, we 

 have about 2 X lo"" representing radium heating. From this 

 the allowance of terrestrial radium per square centimetre 

 inwards is 2.3x10-° grams. This would give a major 

 limit. But it is almost certain that some of this radium 

 is located in more deeply seated parts of the earth. If we 

 take 10- ° as contained in the normal radio-active surface 

 layer, and assume (what according to my experiments 

 should not be far from the truth) that the average radio- 

 activity is 3, we arrive at a thickness of 12 kilometres. 



Some such mean value is necessitated by the evidence 

 we derive from the radio-activity of igneous rocks. These 

 rocks must in many cases be derived from considerable 

 depths. Such outflows as the Deccan may indicate local 

 sub-crustal conditions ; so also may the eruptions of certain 

 volcanic areas. But those extrusions which have attended 

 mountain building, more especially its closing phases, 

 appear to indicate general conditions, and involve the 

 existence of such radio-active materials at considerable 

 depths. If we assume a thickness for the radio-active 

 part of the crust much less than the 12 kilometres, difficul- 

 ties are met with on this line of reasoning.^ 



Proceeding now to the derivation of the results given 

 in the table, p. 464. The equation kB = gbx(D — xl2) (where 

 $ is the temperature at the depth x, D being the total 

 depth of the radio-active layer, q the radium per c.c. in 

 grams, h the heat output of one gram of radium per 

 second, k the thermal conductivity) is easily derived bv 

 considering the conditions of thermal flow in the layer, 

 sunposed to lose heat only at the surface.'' 



The aggregate depths of radio-active material in the 

 several cases of sedimentary deposit assumed in my 

 address amount to 18, 20, 22, 24, and 26 kilometres. I 

 assume the mean radio-activitv to be 3-5, and the average 

 conductivity to be 4Xio-\ From this "the basal temoera- 

 tures are found, as due to radio-thermal actions. These 

 temperatures are to be augmented by the temperatures 



1 Phil. Mag., XXXV., p. 173. 2 Trans. K.D.S., vi., p. 208, 



■' See p. 464, anU, and foot-note as bearing on the possible displacement 

 of the geotherms. 



•* SeeStrutt, Proc. R S., Ixxvii., p 482. 



NO. 2028, VOL. 78] 



proper to the several depths, which depend upon the 

 conducted interior heat. To estimate these we require to 

 apportion the observed average surface gradient (taken as 

 32 metres per degree) between radio-active effects in the 

 upper layer and the flow of heat from within. The radio- 

 thermal gradient comes out at about 75 metres ; the inner 

 gradient is accordingly 56 metres. Hence the total ■ 

 temperature at the base of each radio-active mass is J 

 obtained. But the geotherms proper to the several depths, 

 18, 20, &c., kilometres, under conditions prevailing else- 

 where in the crust, are easily found from the value of 9 

 for the normal layer (82° C), and adding the temperature 

 due to interior heat. From the difference of the tempera- 

 tures we, finally, find the rise of the geotherms. 



As conveyed in my address, I have found on several 

 different values of the thiclcness and radio-active properties 

 of the surface layer, results in every case showing large 

 values for the rise of the geotherms. The data assumed 

 above are by no means the most favourable. 



NOTES. 



It is with deep regret that we learn of the sudden death 

 of Prof. Alexis Hansky, whose work in solar physics at 

 the Pulkowa Observatory has attracted so much atten- 

 tion. According to a letter from M. Tikhoff, which 

 appears in the September number of the Bulletin de la 

 Sociite astronomique de France, M. Hansky was drowned 

 whilst bathing in the Black Sea at Simeise, in the 

 Crimea, on August 11 (July 29 O.S.). The deceased 

 astronomer commenced his practical work in solar physics 

 by observing the total eclipse of 1896 at Novaya Zemlya, 

 and at the time of his tragic death was engaged in the 

 installation of a new observatory in the Crimea which 

 had been given to him, and which he had handed over 

 to the Pulkowa Observatory. By his death at the early 

 age of thirty-six years, the study of solar physics has 

 suffered a loss which it will be exceedingly difficult to 

 repair. 



The President of the Local Government Board has 

 arranged for the making of the two following re- 

 searches : — a chemical and bacteriological investigation, by 

 Mr. C. G. Moor and Prof. R. T. Hewlett, as to the 

 influence of softening and of other chemical processes on 

 the purity of water supplies from the chalk as shown in 

 actual experience and under experimental conditions, and 

 an investigation by Prof. Sidney Martin, F.R.S., into the 

 powers of production of disease possessed by certain 

 streptococci and by the poisonous substances produced by 

 them, in continuance of previous investigations by him on 

 the same subject. These investigations complete the 

 allocation of the scientific grant for the year 1908-9. 



Prof. Robert Koch has been chosen to represent the 

 German Government at the forthcoming International 

 Tuberculosis Congress at Washington. 



The annual conference of the Sanitary Inspectors' 

 Association opened on Tuesday last under the presidency 

 of Sir James Crichton-Browne, F.R.S. 



The third International Philosophy Congress has been 



in session at Heidelberg during a portion of the past 



week. The next meeting will take place in 1912, at 

 Bologna. 



The arrangements for the fourth International Fislieries 

 Congress, which, as has already been announced, is to 

 be held at Washington from September 22-26, are now 

 complete. An attractive itinerary has been arranged for 

 the week following the sessions of the congress, and 



