18J5.] 



|THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



325 



1843 till now, continued observations have been made on llie Atlantic at 

 Skerryvore and neighbouring rocks, lying off the island of Tyree, Argyll- 

 shire. And in 1844 a series of similar oljserviilions was begun on the 

 German Ocean at the Bell Rock. It will be seen, that in selecting these 

 localities a varied exposure has been embraced, comprising the compara- 

 tively sheltered Irish Sea, the more exposed eastern shore of Scotland, and 

 the wild rocks of Skerryvore, which are open to the full fury of the At- 

 lantic, the far distant shores of North America being the nearest land on 

 the west. 



In the Atlaxlic Ocean, according to the observations made at Skerryvore 

 rocks, the average of results for five of the summer months during the years 

 1S4S aiul 1844, is 611 lb. per square foot. The average results for six of 

 the winler months (1843 and 1844), is 20801b. per square foot, or thrice as 

 great as in the summer months. 



The Createst result yet obtained at Skerryvore was during the heavy 

 westerly gale of 2aih March 184.5, when a pressure of C983 lb. per square 

 foot was registered. The next highest is 5323 lb. 



In the Gtim«« Oct'rtH, according to the observations made at the Bell 

 IJock, the greatest result yet obtained is 3013 lb. per square foot. 



It thus appears, that the greatest ellect of the sea, which has bfen ob- 

 served, is that of the Atlantic at Skerryvore, which is nearly equal to three 

 tons per square foot. 



These experiments, amounting to 207 in nHmber,t and on the Atlantic 

 alone extending over 23 months continuously, are not intended to prove 

 anything farther than the simple fact, that the sea has been known to exert 

 a force equivalent to a pressure of three tons per square foot, however 

 much more. 



Ascertained effects of W(cies. 



I shall now contrast the indications of the JMarine Dynamometer by 

 stating a few facts regarding the ascertained effect of the waves in the 

 elevation of spray, and in the transportation of heavy masses of rock. lu 

 the first instance, to give some idea what may be looked for in compara- 

 tively small expanses of water, such, for instance, as the lakes of North 

 America, which, however, exhibit during gales of wind, all the character- 

 istics of an open sea. In the northeastern corner of Lake Erie, the 

 HARBOUR OF BiFFAi.o was constructed at a cost of about 40,000/. It is 

 mentioned in the " i ivil-Eugineering of North America," that the author 

 " measured (at this harbour) several stones which had been moved ; and 

 one of the largest of them, weigiiing upwards of half-a-ton, had been com- 

 pletely turned over, and lay with its bed or lower side uppermost." In 

 the FiiiTH of Forth, at the Guanton Pier works, on the 19lh December 

 1S36, after a gale from the north-east, one stone was moved measuring 

 fifteen cubic feet, or about one ton in weight, and thrown on the beaclf 

 after having been built into the wall; and a stone containing eighteen 

 cubic feet was moved thirty feet from its place ; while the pierres perdues 

 or mound-stones were washed down to a slope of about 4 to 1. The fol- 

 lowing instance, which occurred at the landing slip of the Calf Point 

 Isle of Man, alibrds a proof of the great force of the waves even in the 

 Irish Sea. During a gale from the north-west, a block was lifted from its 

 place in the wail and thrown landwards, which measured 123J cubic feet 

 equal to about 10 tons weight. At the island called the Barrahead, one of 

 the Hebrides, a remarkable example occurred during a storm in January 

 1836, in the movement of a block of stone, which, from measurements 

 taken on the spot, is 9 feet x 8 feet x 7 feet = 504 cubic feet, which, 

 allowing 12 feet of the gneiss rock to the ton, will be be about 42 tons 

 weight. This great mass was gradually moved 5 feet from the place 

 ■where it lay, having been rocked to and fro by the wa\ es till a piece broke 

 off, which rolling down, and jamming itself between the moving mass and 

 the shelving rock on which it rested, immediately stopped the oscillatory 

 motion, and thus prevented the farther advance of the stone. 



Experiments.— With reference to the following experiments I have only 

 to observe, that those which were made at Little Ross, upon the Irish Sea 

 cannot, from the unusual fineness of the weather at the time, be regarded' 

 as affording a true value of the effects of a hard gale in these seas" Of 

 the others it is to be noticed, that where two or three instruments were for 

 some time employed as a check upon each other, and only one or two 

 readings are given, the want has occurred either from the instruments 

 being under repair, or being difhcult of access in stormy weather, or during 

 neap tides. It often happened also, in consequence of the springs provin-- 

 too weak, when new ones had to be made, or the area of the disc reduced". 

 Registers of the state of the weather, apparent height of spray, &c., were' 

 generally kept ; but it was not considered necessary to complicate the 

 Tables by inserting these, excepting in one or two instances. 



A more exposed point of the Skerryvore Rock was chosen for the ex- 

 periments of the second table ; and with the view of ascertaining the effect of 

 the waves at ditferentheights upon the rock, two instruments were fixed the 

 one (No. I.) several feet lower, and above 40 feet seaward of the other (No. 

 II.) It was observed, that about half-flood the waves were a good deal 

 expended before they reached the place where No. I. was placed, from 

 there being so little water on the rocks outside. Whereas when the tide 

 was higher the waves were, from the greater depth of water, not so much 

 broken when they reached No. II. The results of the Marine Dynamo- 

 meter shew generally about twice the force at No. II. as at No I - a 

 result which shews how important it would be to ascertain the relative 



»pw.' "" ""' """'^'" "'""onr to give aU the observations In the Ubl.appeniltd to this 



forces of the waves at different levels upon our breakwaters and other 



seaworks. 



The obsen-atinns nt the Skerryvore lioch; and the neighbouring Island of 



Tijree, distant 13 miles from the fllcerryvore, are as follows : 



Table I. 



Feb. 6 



., 24 



March 11 



Heavy sea 

 lieavy ground a 

 Fi-esh gftles . 

 Fresh breezes 

 Short s 



1 otrong gale, the highest waves sup- •) 

 < nosed 20 feet high, and the spray I 



Pressure in lb. per Ft 



856 3042 



1256 3802 



1028 



From the Transactions of the Royal Society of Edinburgh. 



TIDAL HARBOURS. 



Report of the Royal Commissionirs. 



on\"hrr.n!fHv"""''/''.r'' f f'","" ^^'^'""''^ °^ ""= ^'^°'^ "^ ">e Commissioners 

 on the condition of the Harbours of Refuge in the United Kingdom-we 

 propose at present to continue with the Report on Tidal Harbours 



The various points of inquiry to which the attention of the commission 

 was directed in the instructions given to them for their guidance may be 

 conveniently classed under four heads, viz — 



or nS;^ltri'verl!''' "''"^" '""■' ''^''^ '^^^'^ '° ""^ "^ "^^ tidal harbours 



What encroachments have been made upon them ; by whom and by what 

 authority so made ; and the effect that such encroachments have produced 

 or may hereafter produce. ^ u"">.c>i 



What injury may have been done to those harbours and rivers, or may 

 accrue to them by neglect, or by the unauthorised removal of shingle or 

 other materials from the shores, or by the improper discharge of ballast, or 

 by the drauiage of mines, or by the diversion of their tides or streams. 



becond/y.—\\ hat measures are necessary as well to abate any of the said 

 injuries as to prevent any future mischief.' 



Whether there are sutficient legal powers for enforcing such remedy, and 

 If not what further powers are necessary. 



rkirdly.~lo inquire into the state of the law as regards the powers o£ 

 he Lords Commissioners of the Admiralty for the conservatiou of all the 

 harbours, shores, and rivers of the United Kingdom. 



How far the powers conceded to particular authorities or persons, by 

 charter or by royal grant, or by Act of Parliament, may be held to super 

 ^ vvi?'' ^ '"'^'■'''^''fi ™'"' the jurisdiction of the Admiralty. 



Whether any, and what, legislative measures are necessary to give the. 

 Lords Commissioners of the Admiralty sufficient powers to remove any pre- 

 sent or future encroachments, and to prevent llie construction of anv works 

 which may have an injurious effect on any harbour, shore, or navigable river. 

 Lastly.— 1o inquire what measures it may he expedient to adopt for the 

 general improvement of the harbours and rivers of the United Kingdom. 



The River Clyde and Harbour of Clasyow. 

 From the reports o f Smeaton, Golborne, and Watt it appears that, about 



hppn^hnmH,".^"^?,'""' '■* f'u""'^ """^ Slightly moved, and 14 scattered, all of nhich had 

 J^H , H ,. '^' "■"""'l-bead or end of Hynish Pier, which was still in an unfinished 

 Btate and a Dynamometer wluch was attached to the Pier, registered on tliis occasion 

 about2.„uarrr"'m^'''"%r ' '" 'i '»"'.»"'! exposed. fvhenbuiUi 10 the 3" 

 about i square feet of surface. The stone to which the instrument was filed wan f nm«d 

 upside down, althoush it weighed U ton = 2800 lb. '°"''"°«"' '•"<"' ■"«<» "">» t>"T«« 



43" 



