October 27, 192 1] 



NATURE 



279 



Times of October 17, it is stated that this blasting 

 was sub-let to a firm of contractors and was done 

 by men on piece-work. 



There appear to be at least three commissions 

 investigating the accident : one, appointed by the 

 Reichstag, another by the Bavarian Government, 

 and a third by the Workmen's Council of the 

 Oppau factory, and it is gathered that there is 

 some conflict as to the powers and status of these 

 commissions. An adjournment of the inquiry has 

 evidently been made, but it is not clear as to 

 whether this is for the purpose of obtaining further 

 evidence on the danger of blasting, or, as is sug- 

 gested by the writer of an article in the Chemiker- 

 Zeitung of October 6, on danger that may arise 

 from heating up of the mass through the 



liberation of nitric acid from ammonium nitrate by 

 the acid held as an impurity in the ammonium 

 sulphate. With regard to the latter point, it is 

 stated that the representatives of the factory are 

 taking a continuous record of the temperature of 

 the remaining stock, which amounts to 8,000 tons, 

 with the object of flooding it if any considerable 

 rise occurs. 



In view of the importance of ammonium nitrate 

 and other salts of ammonia for fertiliser purposes 

 on the very largest scale, it is to be sincerely hoped 

 that every endeavour will be made by the Inter- 

 Allied Commission of Control to obtain the final 

 report of the German Parliamentary Committee, 

 together with a record of any experiments con- 

 ducted to elucidate the cause of the explosion. 



The Age of the Earth.* 

 By the Right Hox. Lord Ravleigh, F.R.S. 



T^HE subject which we have met to consider 

 -■- to-day is encumbered with past controversy. 

 It cannot be denied, I am afraid, that exponents 

 of particular views in the past have laid too much 

 emphasis on their own particular way of looking 

 at the problem without making enough allowance 

 for human fallibility. I shall try, so far as pos- 

 sible, to avoid this pitfall. There has been a 

 tendency on all sides for specialists in one 

 branch of science to consider themselves free 

 to disregard evidence drawn from a class of con- 

 siderations with which they are not familiar. I 

 am sure that this is not the road to truth. In 

 attempting a problem of this kind, w^hen we seek 

 to plumb into the depths of time, far beyond 

 human experience, we cannot afford to neglect 

 evidence drawn from any quarter, even if it is 

 not the kind of evidence which we find it most 

 congenial to contemplate. A parallel case is that 

 of a jury of plain men in a murder trial. They 

 may know nothing of medical jurisprudence, post- 

 mortem examinations, and so on. They may even 

 consider the subject repellent ; but that does not 

 exempt them from the duty of fully considering 

 and weighing such evidence to the best of their 

 ability. The witnesses in the trial have, however, 

 to limit themselves to matters with which they 

 are personally conversant. I will try to give my 

 evidence within these limits. 



The phrase "age of the earth," though rather 

 vague, is perhaps definite enough for our purpose. 

 What we want to know is, how long has the 

 earth's surface been fitted for the habitation of 

 living beings? or, alternatively, how long has it 

 taken to accumulate the known series of geo- 

 logical formations? These questions are not the 

 same, but I do not think that we shall need to 

 insist on the distinction this morning. 



Lord Kelvin's arguments depended on attempts 

 to limit the length of time during which the 



1 Contributions to a joint discussion of the Sections of Mathematical 

 and Physical Science, Ge .logy. Zoology, and Botany of the British Associa- 

 tion at Edinburgh on .September i 3. 



NO. 2713, VOL. 108] 



earth's surface temperature could have remained 

 substantially the same as at present, and he 

 attacked this problem from two different points 

 of view. In the first place, he attempted to set 

 a limit of time to the duration of the sun's heat; 

 and secondly, from consideration of the earth's 

 internal heat, he argued back to the time when 

 the surface was too hot for the presence of living 

 beings. I have heard a suggestion that there is 

 some mutual inconsistency in these two lines of 

 argument — consideration of the sun's heat makes 

 the past temperature too low ; consideration of the 

 earth's heat makes it too high — -but I do not 

 think that this criticism is more than superficially 

 plausible. The point was rather that from either 

 of these arguments a condition widely different 

 from the present would be reached, and therefore 

 that, even if there were some unrecognised flaw 

 in one of the arguments, the other would stand. 

 Possibly, looking back into the remote past, a 

 condition of the earth's surface is imaginable 

 where the mean temperature was much the same 

 as at present, heat coming from the earth's in- 

 terior in compensation for a diminished radiation 

 from the sun; but I feel sure you will all agree 

 with me that we cannot get more time by special 

 pleading of this kind. The fossiliferous rocks 

 have, without doubt, been accumulated under con- 

 ditions of solar radiation not essentially different 

 from the present. One simple consideration is 

 that the plants in the coal measures obviously had 

 green leaves, and that these could not function 

 without a full allowance of solar radiation. 



We have then to consider whether Lord 

 Kelvin's arguments can stand in the light of 

 present knowledge. I think we must admit that 

 they cannot. 



First, as regards the earth's heat, it is now 

 generally known that the premises of Lord 

 Kelvin's calculation, carefully particularised by 

 him, are upset by the discovery of radio-active 

 substances in the earth. In 1906 I made a deter- 



