4SS 



NA TURE 



[September 13, 1S94 



Mr. R. G. Halibunon tead a paper on the dwarf races of the 

 New World. 



Rev. \V. H. Beauchamp described the southern visit of the 

 Eskimo, in which he declared thit evidence of Eskimo contact 

 with the Indians of Northern New York were to be found in 

 certain stone knives found among them, specimens of which he 

 exhibited. 



Mr. Dorsey read a paper by William Slurlevant, in which 

 Mr. S:urtevant described three ears of corn from prehistoric 

 grains from localities in Peru, collected by Mr. Dorsey, the 

 especial point of interest being that from a grave of undoubted 

 antiquity in Iquique was found a kind of corn which was com- 

 monly supposed to be of a recent cultivated variety. Mr. 

 Dorsey called attention to the great importance of collecting 

 and preserving all varieties of corn from all prehistoric sources 

 as a means of determining the original habitat of the maize, as 

 well as furnishing an index of civilisation. 



THE DISPLACEMENTS OF THE ROTA- 

 TIONAL AXIS OF THE EARTH} 



"r)ISPL.\CEMENTS of the rotational axis of the earth with 

 reference to fixed directions in space have been observed 

 sine; the earliest ages of astronomical measurement ; for such 

 displacements, visible in wanderings of the pole of the apparent 

 diurnal rotation of the celestial sphere among the constellations 

 of fixed stars, exist in such enormous amplitudes, that in their 

 main features they could be detected by the aid of very simple 

 apparatus and observations. 



The true law and explanation of these wanderings of the pole 

 remained, nevertheless, a deep mystery till Copernicus lifted 

 the veil by showing that they were only the celestial image 

 of real displacements of the rotational axis of the earth in space, 

 and until Newton came and, combining his discovery of uni- 

 versal gravitation with his deduction of the ellipsoidal figure of 

 the earth, proved that these displacements are due to the actions 

 of the moon and the sun on the earth. 



The mathematicians of the eighteenth century completed this 

 explanation by profound researches embracing the full 

 theory of free rotation of a solid system of masses, under the 

 action of various disturbing influences, no! only those acting 

 from outwards on the rotating b^dy as in the case of the sun's 

 and the moon's attractions on the earth), but also those depend- 

 ing upon the condition or changes within the rotating system 

 tself. 



Among several interesting results, thesei nvestigations pointed 

 out an essential difference between the development of the dis- 

 turbed rotation in the first and in the second case. 



Upon the supposition, corresponding to the real terrestrial 

 conditions of the problem, namely, that all the disturbing 

 influences are relatively small in comparison with the amount 

 of energy represented by the primary rotation of the earth 

 itself, the following distinctions were demonstrated. 



Exterior disturbing influences will mainly produce displace- 

 ments of the axis in space, and corresponding wanderings of the 

 pole among the stars, whilst the simultaneous displacements of 

 the axis in the earth itself, in consequence of the particular con- 

 ditions of their evolution, remain insensible. 



On the contrary, interior conditions and disturbing influences, 

 as those contained in the configurations of the masse?, or 

 in changes of the distribution of the masses composing the 

 rotating system, will mainly produce displacements of the rota- 

 tional axis in the rotating body itself, whilst in this case the 

 simultaneous displacements of this axis in space and the corre 

 spending variations of the position of the pole among the stars 

 remain insensible. 



Very soon after these deduclions had been made from the 

 theory, astronomers began to inquire if also effects of the 

 latter type, that i? to say, displacements of the rotational axis 

 ID the earth, really existed. 



According to the theory, such displacements ought even then 

 to exist when the distribution of the masses composing the earth 

 is not in the slightest degree variable. 



It is sufficient for producing such displacements that the 

 position of the rotational axis of the earth is actually not in per- 

 fect coincidence with one of its principal axes of inertia, known 

 as the principal axis. 



' A na|>«r read by I'rof. W. Fo«nitcr. Director of Iht Royal Observatory 

 of Berlin, before the IJrittib A«wci:ttion. 



The slightest deviation of the rotational axis from the principal 

 axis has the consequence that the pole of the rotational axis 

 begins and continues to describe a small circle around the pole 

 of the principal axis. 



The velocity of this movement depends upon the law of the 

 figure and of the distribution of the masses composing the earth, 

 and the best numerical dat.i for this dependence had given the 

 result that the displacement in question would probably have a 

 period of nearly ten months. 



Now all such displacements, possibly measurable with reftr- 

 ence to fixed directions in the earth, and insensible with refer- 

 ence to fixed directions in space, could be found in the most 

 favourable way by measuring as exactly and continuously as 

 possible the distance of the pole from the zenith of the observer's 

 station ; in other words, by repeated determinations of the geo- 

 graphical latitudes. But, notwithstanding very long and relined 

 determinations of the geographical latitudes at some of the 

 principal obiervatories, beginning shortly before the middle of 

 the present century, only very uncertain and discordant traces 

 of the phenomena in question were found. 



The reason for this want of success is now very clear. 

 Astronomers had limited their researches too narrowly to the 

 last-mentioned type, namely, to the supposed regular ten- 

 monthly periodical movement of the pole of the rotational 

 axis around the pole of the principal axis. Too e.isily it had 

 been admitted that all the existing variations of the distribution 

 of terrestrial masses were by far too small for altering sensibly 

 the position of this principal axis itself. 



It was Lord Kelvin, at the Glasgow meeting of the BritisK 

 Association (1874), who at first drew the attention of the 

 scientific world to the consideration of the great natuial 

 transports of masses of air and water and various masses 

 by the water, going on continuously and periodically in the 

 form of currents and circulations of different kind, as well in 

 the atmosphere as in oceans and rivers, for instance the 

 enormous periodical sediments of snow and ice. He showed 

 that these very considerable variations of the distribution of 

 masses on the earih could not only produce sensible displace- 

 ments of the principal axis of inertia, Imt that such displace- 

 ments of this axis could have an amplifying effect on the tol.Tl 

 amount of displacements of the rotational axis. 



For if ihe I'r^ncipal axis were itself not in a constant position, 

 the theoieiiL-aliy required movement of the rotational axis 

 around the principal axis would become a very complicated 

 movement, diffciing entirely from the simple form which to 

 that epoch had appeared in the researches of astronomers. 



This epicyclic character of the movement of the pole of the 

 rotational axis could considerably modify not only the length of 

 the period, but al-o the wh)le geometrical character and ampli- 

 tude of the curve in such a way, that in longer periods epochs 

 of very small variations of latitude could alternate with epochs 

 of considerably increased variations of latitudes. Possibly, at 

 a further consequence of this complication of the displacements 

 of the two axes, and as a consequence of the still existing plastic 

 state of certain parts of the earth, as well as by the damping 

 effects of the fluid parts, even proi^i-iiiiic — ihougli very slow and 

 unsteady progressive — displacements of the rotational axis in 

 the earth could still resul'. 



The field of this research was thus decisively cleared by the 

 veritably releasing ideas of Lord Kelvin. Finally, about four 

 years ago, by the co-operation of some observatories with the 

 International Geodetic Union, clear evidence was obtained, 

 and in the last three years, with the aid of an expedition sent 

 by the International Union to Honolulu, decisive proofs ol 

 such displacements have been found. I consider it a special 

 honour and pleasure to be enabled to submit some of the 

 newest results of this international co-operation to a meeting 

 of the same Association which, twenty years ago, had been 

 witness of the almost prophetic assertions of one of its most 

 illustrious members regarding the real conditions of this 

 important phenomenon. 



I have pr.-pared a diagram (Fig. i, p. 489) showing these 

 newest r suits. ^ ou see in this di.igram a representalion ol Ifie 

 wanderings of the pole of the rotational axis of the earth on the 

 surface 01 the latter during the last twenty months, from 

 October 1892 to May 1S94. 



This sketch is founded on nearly 6030 single determinations 

 of latitude m.ade in the Observatory of Kasan (Eastern Russia), 

 Strassburg (FJsass), and Bethlehem (Pennsylvania). The 

 observations are condensed in twenty monthly mean results, 



NO. 1298, VOL. 50J 



