102 



♦ KNOWLEDGE ♦ 



[March 1, 1887. 



Lastly, on May 15, 1859, the RosetiHwth found in latitude 

 53° 40' south, longitude 123'^ 17' west, an iceberg as large 

 as Tristan d'Acunha. 



When we remember that the icel)erg seen by the Ayncta 

 must have been upwards of a mile and three-quarters thick, 

 we see what amazing masses of ice come forth from the 

 Antai'ctic regions, and liow unsafe it would be for seamen 

 to pursue too scrupulously the great circle course on long 

 voyages in the Southern Seas, seeing that suoli voyages, if 

 piursued, would carry them into regions where ice masses 

 even more portentous than those described would be crowded 

 in even greater profusion. 



Yet, are there no seas where, so far at any rate as east- 

 wai-dly voyages are concerned, the gi-eat circle cour.se seems 

 more inviting than in the southern portions of the great 

 Indian Ocean 1 For there within the " roaring forties," and 

 even far to the south of them, the mighty west winds blow 

 which i-aise the greatest waves which are known in our 

 world. " Between latitude 40" and the ice of the South Pole," 

 says the latest account published of these western vvind.s, 

 " a steady draught of air from the west blows perennially all 

 through the year and all I'ound the globe. It may shift a 

 point or two to north of west, or south, but west it always 

 is ; never sinking below what we call a stiff breeze, and 

 rising often to a gale or half a gale ; and constantly, there- 

 fore, there is a heavy sea, nearly a thousand miles broad, 

 I'olling around the earth from west to east. The waves were 

 magnificent," proceeds Mr. Froude in "Oceana"; "I believe 

 the highest ever fallen in with are in these latitudes. Vessels 

 for Australia under sail alone accomplish often three hun- 

 dred miles a day on the course on which we were going. If 

 they are bound west they keep within the tropics, where 

 these winds do not reach. To steam in their teeth would 

 be impossible even for the most powerful ships afloat." 



Indeed so moved was Mr. Froude by the impressive 

 jiicture presented by this zone of fierce west winds, urging 

 the waters of the sea ever eastwards over the broad span of 

 one thousand miles swept by their strong breath, that he 

 was led to propound what on a latei' page he calls his own 

 wave-theory depending on this phenomenon. I venture to 

 digress for a moment to touch on this theory of Mr. Fronde's, 

 which, as it pi'oved inviting to him, might ba attractive to 

 others, though based in reality on a singular misapprehen- 

 sion of mechanical laws. 



The reader is doubtless aware that, owing to a certain 

 acceleration, or apparent acceleration, of the moon's motion, 

 beyond what the law of gravitation seems capable of 

 explaining, .astronomers have been led to entertain the 

 belief that our earth's rotation, the clock by which we 

 measure astronomical time, may be r\inning gradually 

 slower and slower century after century. The case may be 

 compared to tliat of an apparent acceleration in the speed of 

 a racer, equine or human, timed by a watch not thoroughly 

 trustworthy ; if such a watch were running slow, the timer 

 might very well believe that the racer had gained more in 

 speed than he really had — though perhaps a part of the 

 observed diftcrence might really be duo to an increased 

 velocity. To account for that portion of the moon's 

 increased speed which could not be accounted for by gravity, 

 a very slight diminution of the earth's rotation would be 

 required, corresponding to the loss of much less than a 

 second of time by our terrestrial clock in one yeai'. It has 

 been supiposed that the whole difl'ei'ence may be explained by 

 the action of the tidal wave in a direction contrary to that 

 of the earth's I'otation spin. The French mathematician, 

 Delauuaj', showed, in fact, by a calculation of great pro- 

 fundity, that the tidal wave raised by forces exerted on the 

 earth from without must produce some effect on the earth's 

 rotation. Airy, who at first doubted this, subsequently 



admitted the validity of Delaunay's reasoning ; and the 

 influence of the tidal wave in I'etarding the earth's 

 rotation may be regarded as proved.* But it has 

 become very doubtful whether any letai'dation actually 

 takes place, and it is now generally supposed that the re- 

 tarding influence of the tidal wave may be counterbalanced 

 by some other causes, as yet not definitely determined, by 

 which the earth's rotation may be hastened. Thus the earth's 

 globe may be shrinking in sufficient degree to have its i-ota- 

 tion thereby hastened as much as it is being retarded through 

 the constantly westwardly motion of the tidal wave, (jr 

 there may be other accelerative causes. And just here Mr. 

 Froude steps in with his own wave-theory. It struck him, 

 he said, after describing the waves carried so steadily east- 

 ward by the mighty winds in the South Indian t)oean, that 

 '• a series of enormous waves for ever moving in one direc- 

 tion over so large a part of the earth's surface, might in some 

 degree counteract the force which is slowly stojiping the 

 rotation of our planet. . . . These great waves in the 

 Southern Ocean for ever moving in the opposite direction to 

 the tidal wave, may at least so far counteract it as to add a 

 few million years to the period during which the earth will 

 be habitable." 



But, alas 1 the answer to this is akin to the answer which 

 George Stephenson made to the paradoxist who wished to 

 enforce his own theory of perpetual motion. " All right," 

 said the great engineer, " but before you demonstrate your 

 theory, oblige me by doing what must be very easy to you 

 if you can secure perpetual motion ; take yourself up by the 

 waist-band and carry yourself round this room ; then I will 

 listen to you — with pleasure." The earth is the weight to 

 be rotated, the west winds are the foi'cc by which she is to be 

 moved, and the thousand-miles wide zone of the Southern 

 Ocean is as the waist-band by which she is to be carried 

 round. Unfortunately, though the sun's heat by which 

 winds are raised is an external force, all the mechanical 

 action of winds is earth-boi-n ; for every breath of wind 

 moving northwards there must somewhere be as much 

 moving with equal force southwards ; for every breath of 

 westerly wind an equal force of easterly wind must some- 

 where be exerted. No balance whatever, in one direction 

 or in another, can remain outstanding ; for the law of motion 

 discovered by Newton is not that action and reaction are 

 pretty nearly equal, but that they absolutely and exactly 

 counterbalance each other. The action of the winds is by 

 no means like that of the tidal wave, where the mechanical 

 forces at woi'k have been called into action by the sun and 

 moon, bodies acting on the earth from without. 



These western winds in the southern seas, however, 

 though they do not effectively fan the rotating earth, 

 make the great circle track most advantageous for the 

 seaman travelling towards the east. From Cape Town 

 to Melbourne along a great circle course, the distance 

 amounts to 5,56(3^^ geographical miles, whereas the distance 

 on a rhumb line is no less than G,154 geographical miles, 

 or 587 knots farther. Nearly the whole journey would be 

 favoured by strong westerly winds. An ordinary sailing 



* Mr. Ellerj', Government astronomer at Melbourne, expressed, I 

 SIC, tfic opinion — in conversation with Mr. Froude — th.it the re- 

 tarding influence of flie tidal wave is not proved. Uut liowever 

 skilful Jlr. Ellery may have shown himself as head of an obsor\'a- 

 tory, I have not heard of any studies he has pursued, or any 

 investigations he has published, wliich would make his opinion of 

 weight on a mathematical question of tliis kind, especially where 

 two of the greatest masters of the mathematics of astronomy have 

 been led, after a thorough examination of the evidence, to regard 

 as demonstrated that which Mr. EUcry rejects as still uniiroved. In 

 such cases, " unproved for me " would be the more accurate way of 

 expressing doubt. 



