254 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



[August, 



would be disposed to form the breAkivater foundations below low-water 

 mark with a slope, and above with an upright wall ; was that £8 matter of 

 economy or as matter of principle? — As matter of economy. It is quite a 

 question of the cost. 1 have just finished a design for Holyhead Harbour; 

 there, on account of the facility of getting rough masses of stone for the 

 breakwaters, 1 have proposed to form them of rubble-stone up to low- 

 water mark, with sloping sides. 



If the execution of this work, with the brick blocks, were pressed on so 

 rupidly as to render it necessary that those blocks should be made in re- 

 irole places to be shipped or otherwise transported to Dover, would not a 

 great part, if not the whole, of the economical advantage of using brick 

 masses instead of stone disappear? — To a certain extent it would, but 

 there is no county in Knglaud where briik earth more abounds than in 

 Kent. In short, I am quite satisfied that you must have the material 

 without bringing it by vessel ; it must be brought by railway. 



ON THE ACTION OF M AYES. 



Annex (H), — Prof. Airy's Answers to Questions proposed to liim 

 on the Action of Wares. 



Which form of structure is best adapted to resist the force of ibe waves, 

 an upright wall or a breakwater with a slope similar to that at Plymouth f 

 — In my ju(l;;men', an upright wall. 



You iiave mentioned in a work which I have read with great attention 

 and admiration, on the theory of naves, that the horizontal motion of the 

 particles of water next the bottom, produced by waves in the sea, is found 

 to extend to very great depths, and to occasion a sensible disturbance of 

 slones and sand at the bottom, and that waves break over ridges or shoals, 

 to the depth of 500 feet ?— Yes ; but in these instances the waves are very 

 long. 



Without entering on your theory of waves in the open deep sea, and 

 confining my questions to your deductions from that theory, as to the prac- 

 tical efl'ect of waves on erections in the sea, am I correct in saying you 

 assume, that in deep water the motions of the particles are oscillatory, 

 that the rising and falling of tlie surface of the sea depend on the horiaon- 

 lai movements taking place alternately in the same and contrary directions? 

 — Yes. 



That those displacements are represented by a periodical function, the 

 sine or cosine of an angle depending on time ?^Yes. 



That this circular or elliptical movement of the particles is shown to take 

 place only when a wave is transmitted along a channel of uniform breadth 

 and depth .' — Yes. 



That as the depth of water becomes less, the waves become shorter ? — 

 Yes. 



That their fronts become steeper? — Yes. 



So that as they proceed into water of less depth, their faces become 

 more and more perpendicular until they break? — Yes. 



That waves in a broken stale strike erections in the sea, in a manner to 

 act power'"ulIy and percussively, as hydmulic rams by their momentum ? — 

 ■\es ; when in a broken state they act percussively, not by the ordinary 

 hydrostatic pressure. 



Their mass and velocity give those waves that momentum or percussive 

 force ? — Yes. 



For that reason, in the shallower parts of the proposed harbour, where 

 the waves come into a depth at which, according to your theory, they 

 would by breaking exert such a force upon the wall, you would recom- 

 mend a sloping and not an upright wall? — I should. I think a sloping 

 wall is best able to resist the action of the water in a broken stale ; and 

 inasmuch as you caunot avoid the breaking of the waves, I should recom- 

 mend a slope there ; but in other parts, where you can avoid the breaking 

 of the waves, I would have a perpendicular wall. 



The waves become shorter and shorter as they advance, and, acquiring 

 increasing tendency to break as they come into shallower water, their faces 

 will be nearly vertical, in the state just preceding the broken state. Now, 

 for the reason which you assign for thinking a sloping wall more capable 

 of resisting the impact of a broken wave than an upright wall, do not you 

 think that waves in heavy gales coining in with considerable velocity, and 

 in that stale, would act upon au upright wall with the percussive force due 

 to their weight and velocity, and produce a more serious effect than if that 

 impact were to act against a slope? — It will not strike at all. There will 

 be a great swell up and down again ; there will be nothing like horizontal 

 motion. 



The wave is proceeding? — It becomes a stationary wave; a combination 

 of a direct and a reflected wave. It goes up and down again without 

 breaking ; it is merely an elevation of the surface. I have been in circum- 

 stances where I have had good opportunities of observing that practically, 

 and I know that that is the case. 



Then the modification you would propose is, that in the depth of water in 

 which you think the wave would break, you would recommend a slope, 

 aud in the other part an upright face ? — Yes. 



In what depths, practically, would that be? I think you said the pilots 

 can best answer that. You say that inasmuch as a wave does not break 

 against au upright surface, it will exert no percussive force upon the wall? 

 — No. It will exert the same sort of pressure that there is against a lock- 

 gate ; that 13, a hydrostatic pressure. 



Equal to the weight of a column of water, whose base is the surface 

 pressed, and height the depth of the centre of gravity ?— Yes. 



On the Concare I'lice. — The construction would be exposed to less 

 danger, if the section of the wall presented to the sea a hollow curve, 

 like the base of the Kddystone lighihouse ; but still lliere would be the 

 breaking sea searching through every joint, and nothing can make square- 

 stone masonry quite secure when it is exposed to th s. 



BRITISH ASSOCIATION. 



The seventeenth meeting took pi ice at Oxford on the 23rd June, when 

 Sir IJohert Inglis delivered an elaborate address, which we give in a con- 

 densed form. 



SiK Robert Inclis's Address. 



I begin with Astronorny. — The progress of astronomy during the past 

 year has been distinguished by a discovery the most remarkable, perhaps, 

 ever made as the result of pure intellect exercised he/ore observation, — acd 

 determining williout observation the existence and force of a planet ; which 

 existence and whi-^h force were subsequently verified by observation. It 

 had previously been considered as the great trial and triumph of dynami- 

 cal science to determine the disturbances caused by the mutual action of 

 " the stars in their courses," even when their position and their orbits were 

 fully known; but it has been reserved for these d-iys to reverse the pro- 

 cer-s, and to investigate from the discordance actually observed the exist- 

 ence and the place of the wondrous siranger which had been silently, since 

 its creation, exerting this mysterious power. It was reserved for the,-e 

 days to track the path and to measure the force which the great Creator 

 had given to this hitherto unknown orb among the myriads of the air. 



I am aware that Lalaudc, more than fifty years ago, on two nights — 

 which, if he had pursued the object then first discovered, would have been 

 well distinguished from the rest of the year, and would have added new 

 glory to his own nanie — did observe what is now fully ascertained to have 

 Ijeeii the planet Neptune ; but though I'ranus hail just been added to those, 

 bright orbs which to mortal eyes for more than 2,000 years have been 

 known to circle our sun, Lalande was observing before I'iazzi, Olbers.ai.d 

 Harding had added Ceres, Pallas, Juno, and Yesta to that number, aid 

 before by those discoveries it was proved, not only that the planets round 

 the sun had passed the mystic number of seven — since Herschel had con- 

 futed that ancient belief— but that others might also remain to reward the 

 patient labours of other observers. He therefore distrusted his own eyes ; 

 and preferred to believe that he had been mistaken, rather than that the 

 existence and force of a new planet had been reserved for the discovery cf 

 this latter age. What his eyes saw, but whit his judgment failed to dis- 

 criminate and apply, has since become a recognised fact in science. 



I will not presume to measure the claims of the two illustrious names of 

 Lcverrier and Adams : of him, who, in midnight workings and nalchings, 

 discovered the truth in our own couniry, and of the hardly happier philo- 

 sopher who was permitted and enabled to be the first, after equal workinjis 

 and watchings, to proclaim the great reality which his science had pre- 

 pared and assured him to expect. I will trust myself with only two ob- 

 servations ; the one my earnest hope that the rivalry not merely of the 

 illustrious Leverrier and of my illustrious countryman A<lams, but of the 

 two great nations which they represent, France and England, respectively , 

 may always be confined to pursuits in which victory is witliout woe, aud 

 to studies which enlarge and elevate the mind, and which, if i ightly di- 

 rected, may produce alike glory to God and good to mankind : and the 

 other, my equal hope, that for those (some of whom I trust may now hear 

 me) who employ the same scientific training and the same laborious indus- 

 try which have markeil the researches of Leverrier and Adams, there may 

 still remain similar triumphs in the yet unpenelrated regions of space ; and 

 that — unlike the greater son of a great lather — they may not have to mourn 

 that there are no more worlds to be conquered. 



It is a remarkable fact that the seeing of the planet Neptune was effected 

 as suddenly at Berlin by means of one of the star-maps which has pro- 

 ceeded from an association of astronomers chiefly Germans; such maps 

 forming in themselves a sufficient illustration of the value of such Associa- 

 tions as our own, by which the labour and the expense — too great, perhaps, 

 for anyone individual — are supplied by the combined exertions of many 

 kindred followers of science. 



It is another result of the circulation of these star-maps, that a new visi- 

 tor, a comet, can hardly be within the range of a telescope for a few hours 

 without his presence being discovered and announced through Europe. 

 Those comets which have been of larger apparent dimensions, or which 

 have coiuimied longer within view, have, in consequence, for more than 

 2,000 years been observed with more or less accuracy ; their orbits have 

 been calculated ; aud the return of some has been determined with a pie- 

 cision which in past ages exercised the wonder of nations; — but now, im- 

 proved maps of the heavens, and improved instruments by which the 

 strangers who pass aloug those heavens are observed, carry knowledge 

 where conjecture lately dared luit to penetrate. It is uot that more comets 

 exist, as has sometimes beeusaid, but more are observed. 



Lord Rosse's Telescope. 



An Englishman — a subject of this United Kingdom — cannot refer to the 

 enlarged means of astronomical observation enjoyed by the present age 

 without some allusion to the noble Earl, Lord Rosse, and his most won- 



