5i6 



NA TURE 



[September 20, 1906 



such as might be anticipated. As an illustration of this 

 I will take the Californian earthquake of April 18. This 

 originated along lines of great length on the western side 

 of that country. The reflecting surface I take to be 

 the Sierras, 200 miles distant. A wave group would travel 

 to the Sierras and back in about four minutes, and this is 

 approximately the time interval between the two first large 

 wave groups in the few seisniograms I have of that dis- 

 turbance. 



In offering these suggestions I concur with Dr. Farr 

 that very frequently terminal vibrations of an earth- 

 quake present characteristics suggestive of interference 

 effects, but it is premature to suppose that all the peculiari- 

 ties of a seismogram are to be explained in the same 

 manner. Rhythmical beats at an origin may result in 

 rhythmical beats at a distance. John Milne. 



Shide. Isle of Wight, September 5. 



Remarkable Rainbow Phenomena. 



On Monday, September 3, a very heavy thunder-shower 

 passed from west to east over the parish of Deerness, 

 Orkney, from 5.30 p.m. to 6.25 p.m. When the dark 

 nimljus cloud to the west had lifted its pall, the sun came 

 out in great brilliancy. A rainbow now began to form to 

 the north-east, but instead of the ordinary bow there was 

 one of a bifurcated nature. Two stumps which coalesced 

 on the horizon gradually developed into two magnificent 

 bows, which met on both horizons, viz. north-east and 

 south-west, but were about five or six degrees apart at the 

 apex. All the colours of a radiant bow were present in 

 both, and both had the colours arranged in the order of 

 tlie primary bow. The secondary bow also appeared with 

 the colours reversed and the same bifurcation, but in this 

 case it extended only to about thirty or thirty-five degrees 

 above the horizon, as secondaries generally do. As I had 

 never seen or heard of anything like this, my first impulse 

 was to find a cause. When the double rainbows were at 

 their best, there was a bar of stratus cloud extending 

 across the middle of the sun, and in breadth about one-sixth 

 of its diameter. The two primary bows remained complete 

 from 6.30 p.m. to 6.35 p.m., and without the arc of the 

 apex for about another five minutes. 



At first the bow to the south was the more complete, 

 and finally the one to the north. However, after the sun 

 had crept from behind the bar of cloud there were still 

 double stumps clearly visible. If the cause here attributed 

 be correct, then the only explanation of the bifurcated 

 rainbow being visible after the cloud passed is, that from 

 the points of the heavens where the rainbows were the 

 bar might still be dividing the sun's ravs. Nothing in my 

 meteorological books indicated that this phenomenon had 

 been previously seen. On inquiring as to what others had 

 seen after the thunder-shower, two friends, one five miles 

 and the other three miles almost directly west of me, saw 

 only A perfect bow and its secondary. ' Others nearer the 

 position I occupied saw what they called four rainbows, but 

 had observed neither the coloration nor bifurcation clearly 

 enough for descriptive purposes. M. Spence. 



Deerness, Orkney. 



The Mixed Transformation of Lagrange's Equations. 



Mr. a. B. Basset, in a letter to Nature of August 2, 

 states that the theory of the mixed transformation was 

 first given by himself in 1887, and refers to his treatise on 

 "Hydrodynamics," vol. i., p. 171. If he will kindlv look 

 at my essay for the Adam's prize, pp. 61-4, he will find 

 an elimination similar to that which he speaks of. The 

 resulting modified functions appear to agree term for term. 

 There is also the introduction of a " modified function " 

 by which we can use Lagrange's equations for some of 

 the coordinates and Hamilton's equations for the others. 

 That essay dates from December, 1876, and was published 

 in August, 1S77. The method was afterwards explained 

 without much change in all the editions of mv " Rigid 

 Dynamics" which follow that date, beginning ' with the 

 fourth edition, 18S2. E. J. Routh. 



September 14. 



NO. IQ25, VOL. 74] 



THE RECENT CONTROVERSY ON RADIUM. 



'X'HE recent correspondence on the subject of 



-•- radium, started in the Times by Lord Kelvin, 

 has, after lasting nearly a month and causing 

 widespread interest, apparently closed without any 

 very definite conclusion being reached. Whatever 

 opinion may be formed of the merits of the con- 

 troversy, all must unite in admiration for the bold- 

 ness with which Lord Kelvin initiated his campaign, 

 and the intellectual keenness with which he con- 

 ducted, almost single-handed, what appeared to many 

 from the first almost a forlorn hope against the 

 transmutational and evolutionary doctrines framed to 

 account for the properties of raciium. The weight of 

 years and the almost unanimous opinion of his 

 younger colleagues against him have not deterred 

 him from leading a lost cause, if not to a victorious 

 termination, at least to one from which no one will 

 grudge him the honours of war. If peace and tran- 

 quility now result, and a measure of agreement is 

 arrived at between conflicting views, it will be a 

 result which all concerned will heartily welcome. 

 The most ardent believer in the truth of the new doc- 

 trines cannot be other than satisfied that every feature 

 and assumption that is admittedly speculative should 

 be clearly recognised as such and separated from that 

 which is not, if thereby the experimental foundations 

 of the science of radio-activity are freed from further 

 wordy and unprofitable controversy. There seems 

 now to be a reasonable prospect that this has been 

 secured. 



Lord Kelvin's opening challenge (August 9) was 

 broad and sweeping. He took exception to the state- 

 ment, made by the writer in opening the discussion 

 on the evolution of the elements at the British 

 .Association at York, that the production of helium 

 from radium has established the fact of the gradual 

 evolution of one element into others, and denied that 

 this discovery affected the atomic doctrine any more 

 than the original discovery of helium in cleveite. The 

 obvious conclusion was that both cleveite and radium 

 contained helium. He also stated that there was no 

 experimental foundation for the hypothesis that the 

 heat of the sun was due to radium, and ascribed it to 

 gravitation. 



The challenge was taken up on the other side 

 successively by Sir Oliver Lodge, the Hon. Mr. Strutt, 

 and other well-Icnown authorities, and it soon became 

 apparent that for argument at least Lord Kelvin on 

 his side had to rely practically on himself alone. 

 Prof. ."Xrmstrong, it is true, immediately enrolled 

 under Lord Kelvin's banner, and entered the lists 

 with an embracing criticism of physicists in general, 

 whom, he declared, are strangely innocent workers 

 under the all-potent influence of formula and fashion. 

 He made the statement that no one had handled 

 radium in such quantity or in such manner that we 

 can say precisely what it is, and throughout put the 

 word radium in inverted commas. 



Whether or no his opponents are all as innocent 

 and ignorant as Prof. Armstrong imagines, the fact 

 remains that, except for this ex cathedra utterance 

 and a leading article, argument against the accepted 

 view there was little or none except that contributed 

 by Lord Kelvin himself. Prof. .Armstrong's letter 

 merely served to provide Sir Oliver Lodge with 

 iustification for his favourite theme, which appears to 

 be that whereas chemists have an instinct of their 

 own for arriving at their results, reason is the 

 monopoly of the physicist, whose results the chemist 

 usually manages to absorb in the end. No better 

 argument against the unfairness of this could be pro- 

 vided than by the history of radio-activity itself, which 



