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THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. [September, 



sequently appeared more lustrous than a round one, the hest form was a nar- 

 row flat'sHp, such as window glass readily produced. Mr. Schwabe showed 

 the apparatus used, and the process adopted in spinning the exceedingly 

 minute threads, of which from one to two liundred were used to form a single 

 shoot of the weft. He also showed the mode in which the weaving was 

 performed, which was extremely simple. IMr. Schwahe said that he did not 

 make this communication on account of any novelty in the use of glass, but 

 in the hope of drawing attention to the many new materials which might be 

 used in the manufacture of textile fabrics ; and he produced also some sam- 

 ples of Manilla flax, the fibre of the pina plant, from which a beautifully 

 delicate and transparent cloth could be made. The specimens of manufacture 

 thus produced, though not very perfect at present, seemed to promise more 

 satisfactry results when matured by experience. 



Mr. Hodgkinson explained his apparatus for trying the strength of mate- 

 rials. He brought his apparatus forward, as he had made many experiments; 

 and he was desirous to render them as trustworthy as possible, by convincing 

 the members that every care had been taken to ensure accuracy. Other ex- 

 periments had been rendered unworthy of reliance, from injudicious methods 

 of affixing testing apparatus— as those' of Rennie and Captain Brown in iron ; 

 Girard's experiments, &c. In crushing specimens, it was necessary that both 

 ends should be well bedded, and the pressure transmitted through the axis. 

 To this, other experimenters had not always attended, and by using the 

 pressure of bores directly on the substance to be crushed, they introduced 

 the different errors arising from the pressure being oblique, transmitted 

 through the side, or being exerted on mere points, instead of equally exert- 

 ing its force over the entire top surface : to obviate these objections, he had 

 devised apparatus by which all these errors were avoided. Mr. Hodgkinson 

 explained the crushing apparatus by drawings, &c. In experiments on tear- 

 ing asunder, he had also taken great care, by means of apparatus, which he 

 exhibited and explained, that the strain should be through the axis, and other- 

 wise free from causes of error. Mr. Hodgkinson explained his experiments 

 on torsion, and illustrated his observations throughout by many models and 

 specimens of the substances on which the experiments had been made. 



Professor Moseley asked whether, in the experiments on beams, care had 

 been taken to obvia'te the effects of the friction of the beams on the supports, 

 as this would effect the direction of pressure, altering it from vertical to in- 

 clined, and the neutral line only passed through the centre of gravity of the 

 beam when the pressure was vertical ; also, if care had been taken in laying 

 on the weights, as a weight suddenly laid on produced mathematically twice 

 the effect in deflection. Theoretically, the wtight should be increased by 

 small additions, even as grains of sand. 



Mr. Hodgkinson said he had taken all precautions with regard to the 

 ■weights ; they were added by small portions, and with great care ; the beams 

 rested on tolerably smooth cast iron, on which he believed the friction would 

 be of little importance. 



INSTITUTION OF CIVIL ENGINEERS. 

 April 5. — The President in the Chair. 

 Menai Lighthouse. 

 Desoription. By D. P. Hewett, Grad. Inst. C. E. 



The Menai Strait is peculiarly fitted for a harbour of refuge for vessels 

 entering the rivers Dee and Mersey from the north, and the increasing 

 number of ships frequenting this navigation, as well as the insufficiency of 

 its beaconage, rendered it desirable that the entrance should be distinctly 

 marked ; the Corporation of the Trinity House accordingly decided, in 1834, 

 to effect this object by the construction of a Lighthouse, to be situated on a 

 sunken rock about 200 yards from the Anglesey coast on the west side of the 

 entrance, which is divided by the Puffin Island into two channels, defined by 

 a beacon and two buoys. 



The principal noveltv in the construction of the lighthouse is the base, 

 which, instead of dim'inishing, like the Eddystone, with a regular curve, 

 recedes by a series of rectangular offsets ; the oliject of this form of structure 

 is to break the force of an impinging wave, and prevent the whole effect of 

 its shock being tljrown upon the uiiper part of the building, as it is when 

 guided up bv the curved surface. 



The building, which was designed by Messrs. Walker and Burges, is a 

 handsome circular tower 75 ft. high, 40 ft. in diameter at the base, and 

 20 ft. 6 in. diameter at the top, terminated by a castellated parapet, and 

 entirelv constructed of Anglesey marble. The base of the building is solid 

 to the height of 22 ft. 6 in. from the rock, diminishing at intervals of 2 ft. 

 3 in. bv offsets of 9 in. each, up to ft. 9 in. above high-water mark, where 

 its diameter is 22 ft. Ou that level is the entrance doorway (which is ac- 

 cessible bv steps cut in the base stones). The interior contains six floors, 

 forming rooms for the uses of the light-keepers, stores, &c. Every precaution 

 has been taken to render the exterior joints of the courses water-tight; each 

 stone is secured to tliat below it by a slate joggle, and two oak trenails, 

 passing entirely through it, and entering 8 in. into the lower stone. On the 

 upper bed of each course of stones is a projecting fillet, which fits into a 

 corresponding groove in the under side of the course placed upon it, in order 

 to prevent the water from being forced between the courses. The two upper 



courses project internallv and externally, to form a gallery which supports 

 the parapet and the lantern, the foundation and the framing of which are of 

 cast iron. The wall diminishes gradually in thickness from 6 ft. 9 in. to 2 ft. 

 The communication describes minutely the construction of the floors, the 

 partitions, the stairs, the lanterns, &c., and the proportions of the materials 

 for the mortar, which consisted of three measures of sand, one of ground 

 Ume, and one of Italian pozzuolana. 



The liglit is a stationarv, red, dioptric light of the first order, without 

 mirrors. The burner consists of four concentric wicks, of which the largest 

 is 3i in. diameter ; its ordinary consumption of oil is one pint per hour. The 

 various bearings are given from which the light is visible at sea. After 

 deducting all expenses, the surplus revenue derived from the light dues, 

 during the year 1840, is stated to have been £388 13s. 3d. The lighthouse 

 is connected with the shore by a foot bridge, which consists of a platform 

 2 ft. 3 in. wide, supported upon a series of iron columns placed 10 ft. apart, 

 secured into the rock, and strengthened by stays. This sUght construction 

 has withstood the violence of the waves for three years. 



The paper notices the buildings which have been erected on the shore for 

 the residence of the light-keepers, and then proceeds to describe the beacon 

 before alluded to, which points out a dangerous ledge of rocks on the oppo- 

 site side of the channel. It consists of a cone of masonry, 20 ft. in diameter 

 at the base, and 37 ft. high, surmounted by a staff and globe rising 13 ft. 

 above the apex of the cone. The globe, which is 4 ft. diameter, is formed 

 of copper bands, and is 36 ft. above high-water mark. 



The whole amount expended in these different constructions is stated to 

 have been about .€12,800. The communication was illustrated by a series 

 of detailed drawings and a chart of the straits. 



April 12.— The President in the Chair. 

 On Breakwaters. 

 " Observations upon the Sections of Breakwaters as Iieretofore constructed^ 

 with suggestions as to modifications of their forms." By Lieut.-Ool. H. U. 

 Jones, R. E., Assoc. Inst. C. E. 



This communication is the result of several years' observation of the effect 

 of storms upon the sea faces of breakwaters and piers ; those principally 

 alluded to, and of which drawings were exhibited, were Plymouth Kings- 

 town, Howth, Ardglass, and Dunmore ; a section was also given of the sea 

 wall of the Kingstown Railway, and of the mole of St. Jean de Luz. 



The mode of building with " Pierre perdue" appears to have been brought 



into notice about the time of Louis XV., when the cones at Cherbourg were 



sunk, and filled with stones as a foundation for a wall ; since then the general 



method of constructing sea-defences has been to throw down masses of stone, 



allowing them to form their own angle, subject to the effect of the sea in 



giving them a greater or less slope. In many instances this rough foundation 



has been paved down to below the low-water mark with squared blocks of 



stone secured with much care, and above tliis a wall is built of solid masonry, 



generallv with a considerable slope on the sea face. The author contends 



that thesvstem of assimilating the sea face of breakNvaters to the form ot 



the shore 'at low water is erroneous, because the sea shore is the line ot least 



or non-resistance, not opposing, but yielding to the sea. He asserts that, as 



far as he can ascertain, no pier or breakwater constructed with a sea slope 



has been found to resist the effects of storms without considerable repairs 



and expense being subsequently required. He then gives his observations 



upon the several sections, and states tliat the waves have the most violent 



effect at about half tide, hence the stones at that line are first disturbed, and 



then are carried down into the deep water. To parry this evd nearly 



200,000 tons of stone have been deposited on the fore-shore of Kingstown 



Eastern Pier, vet more must still be added. Similar additions have been 



repeatediv mad'e to Plvmoutli Breakwater, with no better effect. At Dunmore 



iron chains have been fixed in the face of the walls to secure them. At 



Howth a slope of 3 to 1 has been found insufficient. At Ardglass the pier 



head and lighthouse have been waslied away. From these and numerous other 



examples, it is argued that piers in exposedsituations with a considerable in- 



ciiuafion of the sea face do not resist the violence of the waves, whereas there 



are manv instances of upright walls having resisted perfectly. As instances 



of this Old Dunlearv Pier is adduced as being nearly perpendicular, yet never 



having been injured' during a long series of years, although quite as much 



exposed as the New Pier, now called Kingstown; Kilrush Pier, although not 



- - ■ • • has resisted all the shocks of the heavy seas which 



built of heavy materials 



break upon it from the Atlantic. ,, 



From these considerations Colonel Jones proposes upon the " Pierre peraue 

 to rise a perpendicular wall from a little below the level of low-water spring 

 tides : this form, he contends, would resist the upward pressure of the sea 

 upon the broad bases of the stones, and prevent their being removed. He 

 argues that althouch the proposed walls would require to lie built witn 

 squared stones, ins'tead of "Pierre perdue," that the cost would not t)e_ 

 greater than at present, as the area of the section of his proposed %vaii it 

 applied at Kingstown would be oiilv 48G0 square ft., whereas the sectional area 

 of the present pier is 10,085 square ft. The French appear to have partially 

 adopted this form at the new works at Cherbourg; but he considers this mode 

 of construction objectionable, inasmuch as it leaves in front of the outer tace 

 that part of the breakwater which is most subjected to injury. An extensive 



