EARTH TIDES.

Dominion, Volume 2, Issue 490, 24 April 1909, Page 10

EARTH TIDES.

AN "ALMOST INCREDIBLE ANNOUNCE- ... . MENT." INTERESTING STATEMENT BY SIR. G. ■..■- DARWIN. • ■ ; .. "M. Camille Flammarion, the eminent astronomer, in a letter, makes what he describes as 'tho almost incredible announcement' that it has been established as the result, of recent observations that the earth twice every day experiences general undulations corresponding to tho tides : of tho ocean," says the Paris correspondent of Router. ' "This discovery is duo to obseivations mado at tho Potsdam Observatory by tho astronomer Hooker, who, by moans of special instruments, has ascertained that this apparently solid earth is subject to daily oscillations analogous to the tides, rising and falling twice in every twenty-four .hours. some twenty centimetres, or about eight inches. Theso movements are not noticeable,i any more than is the action of the tides to anyone on board ship at sea. Earthquakes from time to time attract attention .to the instability of tho earth, hut tho idea that between these upheavals tho earth's crust remains firm must bo ■ discarded, sinco the species of tidal oscillation described is continually in progress." The "Morning Post" adds:— "Wo print the above 'almost incredible announcement' as it reaches us, though, with due deference to M. Flammarion, wo venturo to think that it contains little than can bo considered 'almost incredible. , Tho fact that tho attraction of tho moon, which causes such obvious periodic movements in tho liquid oceans, must also produce a similar effect on the solid crust of tho earth has boon recognised by physicists and astronomers for many years. "So far from being regarded as 'almost incredible,' it has been for a long time accepted as im uudoubtcd fact, and several at.tempts have been mado to mcasuro tho sizeof the waves, or, to use the expression gonerally confined to tho ocean, 'tho height of tho earth-tide. , "

Departing Moon—Longer Day. Sir George Darwin mado an interesting contribution to the discussion as to the'.action of tho tides, both of tho sea and tho oarth, at a dinner by tho Author's Club, reported by tho "Telegraph." ' "If tho earth were made of steel, it would bo easy for tho mathematician to calculate how much it would rise and fall with tho tido," ho said. "In fact, it would move up and down one-third as much as if it were .liquid throughout, but we should bo quito unconscious of this movement, becauso wo havo nothing by which to mcasuro it. "My brother and I mado tho attempt some twenty-five years ago, but failed for reasons into which I cannot go. Others sinco then havo mado moro or less successful attempts, and at length Dr.- Hecker, at Potsdam, has succeeded fully, nis apparatus is in a chamber cut out of tho side of a well at 80ft; below tho earth's surface, and he has continued to obtain observations by means of photography day and night for sis years. ■ "Tho amount of vertical rise and fall can bo inferred roughly from Dr. Becker's obsorvations. I darosay it may bo in our latitude about 4in. or Bin., m we could easily porceivo,it if there was any fixed point by which to measure tho movement. _ "Another way in which tho tido has an interesting effect is in 'its influence on tho evolution of tho planetary aud stellar systems. 'In tidal'motion tho inoVement of tho water is subject to friction—slight though it may bo.' This friction acts as a very slow brake on tho earth's rotation. It is almost 'infinitesimal in amount, so small that it has not been moasurod, but yet it must exist, Acting alirayd in ono diicction, tho earth must bo slowly spinning slower. Further than this, as tho friction is duo principally to tno moon, thero must bo a reaction on tho moon, and tho efloct of that reaction is to drive the moon further and further from tho earth. Given tho millions of years which we believe tho solar system to havo existed wo can traco tho history of tbo moon and earth backwards. "If, then, wo follow theso changes backwards, in timo wo reach an epoch when tbo moon was only two or thrco thousand miles frS? frti ; j sa i' that if this taction of tho tides is driving iijo moon awav from the earth now, on going backward in time far enough we must como to a timo when tho moon was closo to tho earth. Such a conclusion is obvious, but tho remarkable fact about this result is that it appears that when tho moon was close to the oarth it always faced tho samo side of tho oarth. llius, tho two bodies moved round together a tW voroJinked together, and tho speed at which thoy spun round was only .three or four hours. "This points clearly to tho idea that in vory early times the moon and eart'i wero one body, which bpun so fast that it broke in two, and that tho smaller body—tho moon —was sent away to where wo sco it now by tidal friction. A though tho moon looks so big m the sky it is small compared to tlio ODrth, being only l-80th part as heavv. This view is now very generally accepted by men or science, and some have even speculated as to what part of tho earth tho moon broko away from. It lias been supKcstod that tho Pacific Ocean 13 tho hole left by tho moon. i will not say that I accept this—l will only say that I do not think wo have any proof of it. "Now, if instead of looking backwards, wo look forwards, we shall find tho earth spinning slower and slower, and the moon going further and further, and at last, when tho day is fifty-fivo times as long as it is now, the mcon will again always faeo tho samo sido of tho earth. "It follows then, that by reasoning from which it is impossiblo to oscapo, wo may traco tho moon from a time uhoii sho nas closo to tho earth to a distant future, wlion sho will bo at an immense distance from itand wo begin with a day of three 01 four of our present hours, and end with a day of fifty-five of our present days."