THE TIDES OF THE EARTH.

Dunstan Times, Issue 2483, 31 May 1909, Page 8

THE TIDES OF THE EARTH.

HOW THE NEW DISCOVERIES WERE MADE.

(By Camille Flammarion.) When I announced the results recently obtained in the study of the tides of the earth’s crust, I added that those results were so extraordinary that they were hardly believable. Yet, if one examines the methods used to obtain these results, if one takes into consideration the minute care with winch tho observations have been made, it becomes impossible to doubt the reality ot the movement just discovered. As everyone is aware,, the ocean tides are due to the attraction of the moon and the sun; their amplitude is known; thenheight in each harbor is calculated together with the corresponding hours, anc. 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 ’periodical movements which result from it. , The fact can only be discovered by deviations from the vertical. Already in 1837 Antoine d’Abbadie experimented tor this purpose, using spirit levels, but failed to notice anything but variations duo to the temperature. In 18 12 Zollner, the astronomer, constructed in Prague a houzontal pendulum, by means of which, no declared, one rvould be able to appreciate deviations from the vertical of 1-1000 of a second of an arc. But the results were somewhat confused. In 1874 M. Bouquet do la Greye, at the time of the observation of the transit of Venus, used on Campbell Island and for the same purpose a pendulum with amplifying scales. lu 1878 Lord Kelvin used a long pendulum and a small galvanometer mirror. Thjs apparatus was improved the following year at Cambridge University hy Messrs G. and H. Darwin, who placed it in water in order to savo it _ from the perturbing influence of the variations of temperature. The sensibility was such that at five yards distance an observer could produce a deviation of the imago by merely throwing the weight of Ins body from one leg to the other. In 1883, in the cellars of the Paris Observatory, M. Wolf repeated the experiences of M. d'Abbadie. All these researches, carefully made, only succeeded in revealing _ variations from the vertical duo to tho diurnal heating of tho sun, the effect of which, by the way, is fifty times greater than that ol the attraction of the moon. Nothing had been established which could bo considered as an effect of the attraction of the sun or the moon. When, at the last sitting of the Astronomical Society of France, M. C. Lallemand, a member of tho Bureau des Longi tudes, and director of the General feurvej of France, explained at my anc with great skill all the experiments made on the matter, ho confessed that for the past twenty years everyone had despaired of discovering anything, and had aban donod tho subject; but that one scientist enthusiastic and indefatigable, Pro fees qi Hecker, of tho Prussian Geodctical Insti tut©, had energetically set to work, firs for twenty-nine months —December 1 1902, to tho end of April, 1905—thci again from April, 1905, to July, 1907, anc established at eighty foot from the groum an apparatus of extreme precision mad< of two horizontal pendulums in a roon where tho temperature (11.7dcg. C.) am tho moisture were strictly the same al tho year round. I should state the deviations which haw to he measured do not as a rule exceei 1-1000 of a second of an arc. At th extremity of a pendulum one metro »i length they produce movements whicl measure only a few hundreds of thou sandths of a millimetre. In other words, they arc imperceptible How could one amplify them to make then visible! By tho mode of suspension of th pendulum, bv mirrors reflecting in th distance one luminous point and record in: photographically the image on a cylinder Never was the inventiveness of scientist more subtly taxed. It is thus that waves were recorded twice a day, like those of the ocean tides These waves have been examined hou by hour, and eventually those were recog nised which were due to solar attractioi and those caused hy lunar attraction. The curves arc neat and am their amplitude is so small that it is in deed wonderful to think that one has man aged to discover them. The results of these concordant compari sons prove that the terrestrial globe pot Besses a certain elasticity—about the sam ns that of steel. It is interesting to not that Lord Kelvin had come to the sam conclusion by his calculations on the prt cession of the equinoxes. If the globe were liquid, tluid, thes tides would be three times stronger. But, however small, these earth tide produce on the surface of the globe a rea undulation which is really astounding, fo calculations show that it reaches 7^in! In other words, twice a day tho groun rises to that amount. Since the tide i double, and manifests itself at the sam time at tho Antipodes,, the diameter r the globe consequently increases under that influence. That wave is constantly turning, an constantly alters tho form of tho ball o which wo live, and which is apparent! immovable. How is it that we do not notice it? Because this continual and slow oscilla tion is effected on the whole surface c . tho globe. To places which are close I -each other nothing varies, and since ou judgments can only be formed hy com narison it. becomes impossible for us t notice the slightest variation. But tho fact remains that all groum

moves, and ceaselessly. The ground is

not homogeneous, and yet it is impossible to find any connection between these earth-tides and earthquakes. If wo are able to observe the ocean-tides it is because of the shores. At sea it is impossible to notice the tide, because there is no point of comparison. But by the seaside wo see the ocean rise and withdraw. The occan-tido moves 60 centimetres m the open sea, and were our glouo entirely covered with water and peopled with sailors tho existence of the tides would have remained unknown. Besides, do we notice the movements of tho diurnal rotation of the earth, which makes all points of the equator run at a speed of almoso 500 yards per second.

Do we notice the annual movement of

the earth, which carries us away into space at a speed of some eighteen miles ner second? We run, wo fly on a celestial automobile at a fantastic rate. Who realises it?

Do we notice that our vessels travel in tho infinite more rapidly in December and January and less so in June and July? Fortunately, everything is built in such a way in ponclero et mensnra (in weight and measure) that wo live quietly on a ground which seems fixed, solid, stable to us, and entirely worthy of confidence. Wo breathe without thinking of it. Our heart beats, our blood travels. That heart has been wound up to give about 100,000 pulsations per day, or 33 A millions per year, or 1825 millions in fifty years. It is to heat one, two. or three thousand millions of times and then stop. Around us everything is in motion, and in ourselves also. In men, in animals, in plants, in minerals even, the atoms are constantly quivering. And the stars, atoms of the firmament. are carried away, like our sun and like ourselves, at such speeds that several of them travel at the rate of 190 and even 250 miles per second ! The law of work is the supreme law. The new motions of the earth now discovered is, no doubt, a cause for wonder.

But there is nothing unusual in it. For everything is in motion, and everything is motion. It also shows us that we have still a great deal to learn, and that science has never said, its final word.