THE TIDES OF THE EARTH.

Grey River Argus, 20 April 1909, Page 4

THE TIDES OF THE EARTH.

HOW THE NEW DISCOVERIES WERE MADE.

(By Camille Flammarion, in DailyMail). When I announced the results recently obtained in the story of the tides of the earth's crust, I" added that those results were so. extraordinary- that they were hardly believable Vet, if one examines t«e methods usjd to obtain these resuls. if one talc ;s into consideration the minute ca:c with which the observations have been made, it becomes impossible to doubt the % reality of the movement iu-,t discovered. , As everyone is aware, the ocean tides are due to the attraction of the mo.)n and the sun; their amplitude is known ; their height in each harbi>y Ss tskuiste^ i&^&ey wii&i the corresponding hours, and it is shown that the observation always agrees with the calculation. Now, for a long time astronomers have been wondering whether this double attraction of the sun and the moon had not an. influence on the terrestrial globe itself, and they have also been trying to discover the periodica 1 movements which might result from it. The fact can only be discovered by deviations from the vertical. Already in 1537 Antoine d'Abbadie experimented for this purpose, using spirit levels, but failed to notice anything but variatious due to the tempera? ture. In 1^72 Zollner, the astronomer, constructed a Prague a horizontal nendulum, by means of which, he -declared, one would be able to appreciate deviations from the vertical of j-1,000 of a second of an arc. But the results were somewhat confused. In 1574 M. Bouquet de la Greye, at the time of the observation of Ihe the transit of Venus, used on Campbell Island one for the same purpose a pendulum with amplifying scales. LORD KELVIN'S PENDULUM. ' •In 1878 Lord Kelvin used a long pendulum and a small galvanometer mirror. This apparatus was improved the following year, at Cambridge Univeisity, by Messrs G. • and H. £>ari Win, who placed it in water in order !to save it from the >pexturbing influence of the variations of temperature. The sensibility was such tnat &t five yard's distance an observer j could produce a deviation of the image by merely throwing the weignt of his body from one leg to the other.'

) the I In ISB2 i in the cellars of the Yvi istryJ Observatory, Mr Wolf repeated 1 mar-/ experiences of M. d'Abbadie. ir as All- these researches, carefully ma scri- on ' v succeeded in revealing variatio 8, to from the vertical due to the diurr feet heatin 8T of the sun, the effect of whi gton by the way > is fift y times- great >y a an that of the attraction of t; gl6 moon. Nothing had been establish! . ne which couM be considered as an t | t of feet of the attraction of the sun < B 0 the moon. lr a When, at the last sitting of tl Ore- Asti cnomical Society of France> h ould a member of the Bu •ate. eav es Longitudes and director c Mr. tne G enera l Survey of France, explaii pine ed at mv request and with great ski He at the experiments made on the mal , ant l er, he confessed that for the past 2 years everyone !had despaired of dis the covens' anything and had abandomei tsed the s . ub J' ect ; but that one scientist iv^ . enthusiastic and indefatigable, Pro ons' * esso ? H «ok€(r, of the Prussion Geode 2 . g ical Institute, had entergetically se "j n to work, first for twenty-nine month! oa ~ December 1 1 1902, to the end of Ap ere ril I ?° S to J uly IQ ° 7 > and «stablishec Hcv at •■• eiffhty f( ? c^ above -the ground ar 't apparatus cf extreme precision made of of two horizontal pendulums in a room where the temperature (11.? deg j e( j C.> and the nzcistarc «'ere scrict- , . ly the sarae the year round. I should state the deviations which s have to be measured do not as a rule irv exceed 1-100 of a second of an arc. )n - At the extremity of a pendulum oac !nt metre in length they produce move--r" mento which measure only a few IC - hundredths of thousandths of a millia" metre ! n " In other words, they arc imper"e ccptiblc. How could one .-amplify he them to make them visible ?' By the jd mode of suspension of the pendulum, m by mirrors reflecting ujt, the distance m ;one luminous point and . recordingP- phctcgraphically the image on a cylinder Never was the inventiveness s- of scientists more subtly taxed h RECORDING OF THE ' WAVES. t- Ir is thus that waves were recordn cd. twice a day, like tnose of the ocs Pan tides. These wares have been ° hour by hour, and evenu*ally those^were recognised which were £•■ due- to- solar attraction' aricI J "thQse d caused by lunar attraction. '\ } '•■ « :The curves are neat"' and Qjrecise, v ;f na i their amplitude ; is; so small that j -.it.-is indeed wonderful ', to think that y 'discover them} The result of these concordant compafisons prove" that the" 'terrestrial ' r - glbibfei]>bssesses a certain - elasticitv — a [- bbut the same as that of, steel. It' . is interesting- toy note that Lord Kel- \ yin had come to' the ;samej cqnclusion . as his calculations on the;, iwecei'ssdon of 'the equinoxes-. 1 ' i ■■' is. i lf ; the globe were liquid, fluid," these tides would be three times stfpnger. : ' ■Riiii however smalh . these earthtides produce on the surface"' of ""the globe a real undufartion which; is real1 V astounding, -for calculations '■. show that it reaches >Jin r ■ V:. 1 ;V' r ' In other words, twice a day the Rfrriund rises to : that amount."Since the tide, is double, and manifests-it- . self, at' t(he same, time; ait the^ntipodes, .the "diameter, of the globe conse-.qu.c-ntly'*increase .is^in unde'fojhat in.fluence. ; ;•;;,. . : . ■■■: \ Wi That wave is constantly, turning, and c6ns;ta]itly , alters dihe forimi of the.ball dri which we live, andjiwhich is apparently immovable. ' N How is 1 it we. do npt notice ft r . . i Re cause this,, continual slow • oscillation is effected on the whole- \ surface of . the giabe. To .places ; 5 .which are closs to each other noth- f ing varies, and since our judgments can only He formed b v y comparison it beccmes impossible for us to notice' -: the slightest variation. *