December i, 1892] 



NATURE 



t09 



which the sun's lieat is renovated. It is a reasonable supposition 

 that the sun was at that time in the act of receiving a more than 

 usual accession of new energy ; and the theory which assigns the 

 maintenance of its power to cosmical matter, plunging into it 

 with that prodigious velocity which gravitation would impress 

 upon it as it approached to actual contact with the solar orb, 

 would afford an explanation of this sudden exhibition of intensi- 

 fied light, in harmony with the knowledge we have now attained, 

 that arrested motion is represented by equivalent heat." 



It has certainly been a very tempting hypothesis, that quanti- 

 ties of meteoric matter suddenly falling into the sun is the cause, 

 or one of the causes, of those disturbances to which magnetic 

 storms on the earth are due. We may, indeed, knowing that 

 meteorites do fall into the earth, assume without doubt that 

 much more of them fall, in the same time, into the sun. Astro- 

 nomical reasons, however, led me long ago to conclude that 

 their quantity annually, or per century, or per thousand years, 

 is much too small to supply the energy given out by the sun in 

 heat and light radiated through space, and led me to adopt un- 

 qualifiedly Helmholtz's theory, that work done by gravitation 

 on the shrinking mass is the true source of the sun's heat, as 

 given out at present, and has been so for several hundred thou- 

 sand years, or several million years. It is just possible, how- 

 ever, that the outburst of brightness described by Lord 

 Armstrong may have been due to an extraordinarily great and 

 sudden falling in of meteoric matter, whether direct from extra- 

 planetary space, or from orbital circulation round the sun. But 

 it seems to me much more probable that it was due to a refreshed 

 brightness produced over a larger area of the surface than usual 

 by Ijrilliantly incandescent fluid rushing up from below, to take 

 the place of matter falling down from the surface, in consequence 

 of being cooled in the regular regime of solar radiation. It 



-..^ seems, indeed, very improbable that meteors fall in at any time 

 to the sun in sufficient quantity to produce dynamical distur- 



^ bances at his surface at all comparable with the gigantic storms 

 actually produced by hot fluid rushing up from below, and spread- 

 ing out over the sun's surface. 



But now let us consider for a moment the work which must be 

 done at the sun to produce a terrestrial magnetic storm. Take, 

 for example, the "^ agnetic storm of June 25, 1885, of which 

 Adams gives particulars in his paper of June, 189 1 (Phil. 

 Trans., p. 139 and PI. 9). We find at eleven places, St. 

 Petersburg, Stonyhurst, Wilhelmshaven, Utrecht, Kew, Vienna, 

 Lisbon, San Fernando, Colaba, Batavia, and Melbourne, the 

 horizontal force increased largely from 2 to 2.10 p.m., and fell 

 at all the places from 2.10 to 3 p.m., with some rough ups and 

 downs in the interval. The storm lasted altogether from about 

 noon to 8 p.m. At St. Petersburg, Stonyhurst, and Wilhelms- 

 haven, the horizontal force was above par by o 00075, o"ooo88, 

 and 0-00090 (C.G.S. in each case) at 2.10 p.m. ; and below 

 par by 00007, o-ooo66, 0*00075 at 3 o'clock. The mean value 

 for all the eleven places wasnearlyo'0005 above par at 2h. lom., 

 and 00005 below par at 3h. The photographic curves show 

 changes of somewhat similar amounts following one another 

 very irregularly, but with perfectly simultaneous correspondence 

 at the eleven different stations, through the whole eight hours of 

 the storm. To produce such changes as these by any 

 possible dynamical action within the sun, or in his atmo- 

 sphere, the agent must have worked at something like 160 

 million million million million horse-power^ (12 x 10'' ergs per 

 sec), which is about 364 times the total horse-power (3*3 x 10^' 

 ergs per sec.) of the solar radiation. Thus, in this eight hours of a 

 not very severe magnetic storm, as much work must have been 

 ■done by the sun in sending magnetic waves out in all directions 

 through space as he actually does in four months of his regular 

 heat and light. This result, it seems to me, is absolutely con- 

 clusive against the supposition that terrestrial magnetic storms 

 are due to magnetic action of the sun ; or to any kind of dyna- 

 mical action taking place within the sun, or in connection with 

 hurricanes in his atmosphere, or anywhere near the sun outside. 

 It seems as if we may also be forced to conclude that the 

 supposed connection between magnetic storms and sun-spots is 

 unreal, and that the seeming agreement between the periods 

 has been a mere coincidence. 



We are certainly far from having any reasonable explanation 

 of any of the magnetic phenomena of the earth ; whether the 

 fact that the earth is a magnet ; that its magnetism changes 

 vastly, as it does from century to century ; that it has somewhat 

 regular and periodic annual, solar diurnal, lunar diurnal, and 

 ' I horse power = 7 46 x io9 ergs per second. 

 NO. 1205, VOL. 4.7I 



sidereal diurnal variations ; and (as marvellous as the secular 

 variation) that it is subject to magnetic storms. The more mar- 

 vellous, and, for the present inexplicable, all these subjects are, 

 the more exciting becomes the pursuit of investigations which 

 must, sooner or later, reward those who persevere in the work. 

 We have at present two good and sure connections between 

 magnetic storms and other phenomena : the aurora above, and 

 the earth currents^ below, are certainly in full working sympathy 

 with magnetic storms. In this respect thq latter part of Mr. 

 Ellis's paper is of special interest, and it is to be hoped that the 

 Greenwich observations of earth currents will be brought 

 j thoroughly into relation with the theory of Schuster and Lamb, 

 i extended, as indeed Professor Schuster promised to extend it, 

 to include not merely the periodic diurnal variations, but the 

 irregular sudden changes of magnetic force taking place within 

 any short time of a magnetic storm, 

 j In my Presidential address of last year I referred to the action 

 I of the International Geodetic Union, on the motion of Prof. 

 ' Foerster, of Berlin, to send an astronomical expedition to 

 ' Honolulu for the purpose of making a twelve months' series of 

 j observations on latitude, corresponding to twelve months' 

 I simultaneous observations to be made in European observatories ; 

 I and I was enabled, through the kindness of Prof. Foerster, to 

 i announce as a preliminary result, derived from the first three 

 \ months of the observations, that the latitude had increased 

 : during that time by ^ sec. at Berlin, and had decreased at 

 Honolulu by almost exactly the same amount. The proposed 

 year's observations, begun in Honolulu on June I, 1891, were 

 \ completed by Dr. Marcuse, and an elaborate reduction of them 

 ' by the permanent Committee of the International Geodetic 

 i Union was published a month ago at Berlin. The results are in 

 j splendid agreement with those of the European observatories : 

 Berlin, Prag, and Strasbourg. They prove beyond all question 

 j that between May 1891 and June 1892 the latitude of each of the 

 three European observatories was a maximum, and of Honolulu 

 a minimum, in the beginning of October, 1891 : that the 

 latitude of the European observatories was a minimum, and of 

 Honolulu a maximum, near the beginning of May, 1892 : and 

 that the variations during the year followed somewhat approxi- 

 mately, simple harmonic law as if for a period of 385 days, with 

 range of about \ sec. above and below the mean latitude in 

 each case. This is just what would result from motion of the 

 north and south polar ends of the earth's instantaneous axis of 

 rotation, in circles on the earth's surface of 7*5 metres radius, at 

 the rate of once round in 385 days. 



Sometime previously it had been found by Mr. S. C. Chandler 

 that the irregularvariationsof latitude which had been discovered 

 in different observatories during the last fifteen years seemed to 

 follow a period of about 427 days, instead of the 306 days given 

 by Peters' and Maxwell's dynamical theory, on the supposition 

 of the earth being wholly a rigid body. And now, the German 

 observations, although not giving so long a period as Chandler's, 

 quite confirm the result that, whatever approximation to follow- 

 ing a period there is, in the variations of latitude, it is a period 

 largely exceeding the old estimate of 306 days. 



Newcomb, in a letter which I received from him last Decem- 

 ber, gave, what seems to me to be, undoubtedly, the true ex- 

 planation of this apparent discrepance from dynamical theory, 

 attributing it to elastic yielding of the earth as a whole. He 

 added a suggestion, specially interesting to myself, that investiga- 

 tion of periodic variations of latitude may prove to be the best 

 means of determining approximately the rigidity of the earth. 

 As it is, we have now, for the first time, what seems to be a 

 quite decisive demonstration of elastic yielding in the earth as a 

 whole, under the influence of a deforming force, whether of 

 centrifugal force round a varying axis, as in the present case, or 

 of tide-generating influences of the sun and moon, with reference 

 to which I first raised the question of elastic yielding of the 

 earth's material many years ago. 



The present year's great advance in geological dynamics forms 

 the subject of a contribution by Newcomb to the Monthly Notices 

 of the Royal Astronomical Society of last March. In a later 

 paper, published in the Astronomische Nachrichten, he examines 

 records of many observatories, both of Europe and America, 

 from 1865 to the present time, and finds decisive evidence that 

 from 1865 to 1890 the variations of latitude were much less than 

 they have been during the past year, and seeming to show that 

 an augmentation took place, somewhat suddenly, about the year 

 1890. 



When we consider how much water falls on Europe and Asia 



