42 



NA TURE 



[May 12, I ; 



The Movement of the Earth's Polar Axis iSgo'o- 

 i897'5.— To the Astr. Nachr. (No. 3489) Prof. Albrecht con- 

 tributes a short abstract of an investigation which he has just 

 completed on the path of the earth's polar axis. In a previous 

 number of the same journal (No. 3333) he gave the result of a 

 similar piece of work for the period i890'0-i895'2. The mass 

 of material that has since accumulated has led Prof. Albrecht to 

 reinvestigate the motion from the beginning, or, in other words, 

 to trace the movement of the pole for the whole period iSgo'O- 

 1897 '5. An examination of the resulting curve shows that from 

 the year 1890 to 1895 a decrease in the amplitude took place, the 

 curve towards the time of the latter year being not very far dis- 

 tant from the position of the mean pole. From 1895 the ampli- 

 tude began to increase, but without reaching the value of that 

 attained in the year 1890, The curve during the interval 

 1897 '0-97 '8 approached the mean pole by quite a tenth of a 

 second more than it did during the period i890-o-90-5. Prof. 

 Albrecht consequently points out that since the curve does not 



Movement of ihe north pole of the earth's axis. 



repeat itself after a period of seven years, the orbit of the pole's 

 movement cannot be represented by a term of twelve and of 

 fourteen months period. 



Comparing the observed and calculated values of <^-<f>o, he 

 is led to infer that a part of the series of observations is more 

 or less affected by systematic errors, the great portion being due 

 to refraction disturbances. To remedy this in future it is pointed 

 out that greater care must be taken to ensure equality of re- 

 fraction towards the north and south by having large openings 

 (shutters) in the observing room, and by placing the instrument 

 central as regards the shutters. Further, mention is made of 

 the locality of the observatory, and such positions should be 

 chosen where the land and vegetation conditions towards the 

 north and south do not offer great contrasts. 



Comet Perrine (March 19). — The following ephemeris 

 for this comet is continued from Astr. Nack., 3488. 



Berlin Midnight. 



May 



0-38 



0-33 



During the present week the comet approaches the vicinity of 

 the well-known great cluster in Perseus. 



NO. 1489, VOL. 58] 



The Northern " Durchmusterung."— A committee, 

 consisting of Profs. E. C. Pickering, J. G. Hagen and M. B. 

 Snyder, informs us {Ast7-ophysical Journal, No. 4, April 1898) 

 that a new edition of the Durchmusterung is being prepared by 

 the Bonn Observatory, and will shortly be published, provided 

 that subscriptions for a hundred copies at seventy marks each 

 are promised. The fact that the original edition of this work 

 is exhausted, and that the price asked was exceptionally low, 

 should have induced many libraries and institutions to have 

 taken this opportunity and become possessors of the work. It 

 is stated that after May i of this year the price will be raised to 

 one hundred and twenty marks, so that, if this date be adhered 

 to, the opportunity for obtaining copies at the cheaper price has 

 been missed. 



The Astronomical Society of Wales.— In this column 

 we have several times referred to the excellent work the 

 Astronomical Society of Wales is doing in promoting the study 

 of astronomy and the allied sciences. The Society has just 

 published in a new form and under somewhat new conditions 

 the first issue of their quarterly journal, the Cambrian Natural 

 Observer, which it is hoped will appear regularly. In the 

 introduction we are told, " for some reason or other science 

 does not seem to flourish in Wales ; yet, the opportunities for 

 the observation of natural phenomena — using these words in 

 their broadest sense — are neither few nor unimportant." May 

 the influence of the Society be so effective that such a statement 

 as the above will in the next few years cease to be accurate. 



SEA-BEACHES AND SANDBANKS.^ 



nPHIS paper is the sequel to one on "The Formation of Sand- 

 ^ dunes," in the Geographical Journal, March 1897. It 

 en\bodies a research upon the processes which distribute the 

 detritus which enters the sea at its margin, and upon the 

 behaviour of the material distributed. 



Fine mud settles through water with such extreme slowness, 

 that wherever the bottom is disturbed by waves (say, to the edge 

 of the continental shelf) it cannot anchor itself upon the bottom 

 even during the slack water of the tides, so that the action of 

 gravity is cheated. This leads to the conclusion that the transit 

 of mud down the slope from the shore is not due to the action 

 of gravity, but that the principal factor determining the well- 

 known direction of mud-transport is the diminution of intensity 

 of bottom agitation from the shallows to the depths. 



The usual condition of sea-water is one of oscillation which is 

 not quite symmetrical in amount {i.e. there is often a prevailing 

 drift in one direction), and which is scarcely ever symmetrical in 

 intensity, a short quick motion one way being balanced, as far 

 as the movement of the water itself is concerned, by a long 

 slow motion in the reverse direction. 



The author shows how suitable oscillation on a seaward slope 

 will set shingle travelling shoreward, and sand simultaneously 

 travelling seaward. The condition of the transport of shingle 

 (great intensity of motion) keeps most of it close against the 

 shore, often in a bank or beach ; while the inability of mud to 

 settle except where the water is quiet causes it, as we have seen, 

 to accumulate in mud flats beyond the limits of wave-action. 

 The accuniulatioAs of sand are of greater variety, for, although 

 the mean term in size, it possesses a greater independence of 

 motion, or persistence, or effective inertia, than either of the 

 extreme terms. Mud (by which is intended throughout such 

 characteristic marine mud as the well-known "blue mud") 

 obeys each slightest swirl of the water ; it follows almost exactly 

 the stream-lines ; and it is only in the slow settlement of the mud 

 in still water that muddy water behaves otherwise than as an 

 emulsion. Shingle, again, is not raised to any great height from 

 the bottom, and sinks so swiftly that it does not take a long free 

 flight in water. Hence, when it is moving it follows almost 

 precisely the direction of the momentary movement of the water. 

 Sand, on the other hand, is frequently churned up to a con- 

 siderable height from the bottom, and often has a long free path ; 

 but when the stream-lines of the water are suddenly deflected, 

 whether vertically or horizontally, inertia carries the sand on, 

 the stream-lines of the sand being deflected less than those of the 

 water. Similarly, when the current slackens the sand flings 

 itself forwards, as is so noticeable in the rippling of sand by 



1 By Vaughan Cornish, M.Sc. (Vict. Univ.). (Abstract of a paper read 

 before the Royal Geographical Society on March 16, published in the 

 Geographical Journal.) 



