68 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



[Feb. 10, 



the oeacon erected in place by Mr. Benjamin Pomeroy, of Stonington, 

 ConnectU'Ut, under a contract made with him for that purpose. The 

 entire cost of the iron vvorlc and foundation was about 4.,&)0 dollars, 

 anil tlie time consumed in the construction was three months. 



I had it in contemplation at one time to coat the iron work with 

 zinc, by means of electro-galvanism, but 1 found that too mucli time 

 would be required for preparing the necessary tanks and ap|)ar,itus. 

 1 venture to hope, however, that anotlier occasion may present itself, 

 and that in the more important structure of the "screw pile light," 

 which 1 trust 1 shall one day see executed upon our own shores, that 

 the galvanizing process may be successfully ap[ilied. 



In conclusion, I beg to call attention to one or two of the more im- 

 portant advantages which this applicaiion of one of the priiiciples of 

 Mitchell's Screw-pile, (see Cixnl Engivtcr ^- ArchihcCs-Joarnal, p. 182, 

 vol. 3, 1S4U,) to the construction of light houses and beacons, presents. 



In a very exposed situation, a light, or a beacon, if built of masonrv, 

 can only stand when the best description of work is introduced; this, 

 of course, involves great expense, and much time. The mode ot con- 

 struction for such situations must, in principle, be similar to that 

 adopted for the Eddystone and Bell Rock lights, and this, as all know 

 who understand the subject, would, in the case of our own coast, ^xe- 

 aent an insiiptralilc ubjtclion : for example, the Bell Rock Light, on 

 the coast of Scotland, cost £3G0,0UU, and four years were required to 

 build it, this too in a situation where the rock upon which it is placed 

 is bare at low water. The Eddystone was neither so costly, nor did 

 it require so much time to complete it, still the amount would, with 

 us, justly be considered out of the question for a single light.' There 

 are many places upon our coast at which tlie screw pile light could be 

 erected at a very moderate cost, far less, indeed, than that of a light 

 ship ; notwithstanding this, there are at this time several floating 

 lights in Pamlico Sound, on the coast of North Carolina. The Middle 

 Ground, in Long Island Sound, upon wdiich there are only 3 feet at 

 low water, and at which a light boat is now maintained, is, of all 

 others, the most suitable point to make the iirst experimei.t upon with 

 this description of light. 



In reference to the durability of wrought iron exposed to the action 

 of sea water, I have not a great deal of information to impart, still I 

 have some which beais upon this question. Upon many of the reefs 

 in Long Island Sound, and more particularly in Fisher's Island Sound, 

 it lias been the practice tor many ye.irs to erect wiought iron s|)indles 

 of about 4 in. di.imeter, and from 15 to 2jft. in lieight; such spindles 

 last from 15 to 20 yeais, unless carried away by ice. The contractor 

 who placed several of these spindles, informed me that one upon a 

 reef in Fisher's Island Sound hail been up iU years without being re- 

 newed ; the wasting takes place principally between high and low 

 water, and in this particular case, the size of the spindle is reduced 

 from 4 ti) 2 inches in diameter. If, however, the zincing process, or 

 if a |)reci|Utate of copper be resorted to, there is every reason for be- 

 lieving th.a the iron thus protected would last twice, or three times, 

 2iJ years. In short, economy in cost and in time, and the application 

 of the principle of the screw idle in situations where masonry could 

 not be resorted to without inordinate expense, would seem to be ad- 

 vantages in theinsirlves sufficient to justify extensive experiments in a 

 brancii of the public service of such importance as that of our light- 

 house system. 



2 Tile Car Rock Beiit'oii, on tlie coast of Scotland, cost ^S.OOll ; six years were required 

 for tlie construction ; it was intended to build it entirely ol stone, but when half liinshed 

 tlie upper part was constructed of cast iron. The cast iron beacon on Vork Ledge Maine, 

 is ail exact copy of the Car Koclc iieucou : it cost ^'2,000. 



PATENT SCREW-PILE BATTERY AND LIGHT-HOUSE. 



Mr. Mitchfll, the Patentee of the Screw. )iile, previously described in our 

 Journal, proposes to adapt them for tlie purposes of furniing foundations for 

 tlie erectiiv^ of batteries in tlie oi<eii sea, in such situations as the Goodwin 

 Sands, and other sub-marine saiul-lianks. 



The jirinciplc of such foundations has already been well tested both on the 

 east and west coast of England — off the shores of which have been erected, 

 screw-pile light-houses, that have now withstood the storms of several win- 

 ters, without cxhihitini; the slightest symptom of insecurity or decay. The 

 stability of such structures depends on two causes: — Fiist, the tirm hold 

 which the broad screw takes of the ground, by being forced far beneath its 

 surface. And, secondly, the solid part of the building being placed above 

 the reach of the highest sea — no broad surface is opposed to the free passage 

 of the waves — consequently, the structure is not affected by them. 



The first foundation of this description was fixed in the Maplin Sands, by 

 Mr. Mitchell in 1838, by order of the Trinity House, at the recommendation 

 of their engineer, Mr. James Walker, for the Maplin Light-house; and, though 

 it stands upon a bank of loose sand, many miles from the nearest coast, and 



exposed to the swell from the German Ocean, yet it is as stable and likely to 

 endure, as if based upon a rock. But the first light-house of this description 

 was erected by Mr. Mitchell in 1839, at the entrance of the sea reach, leading 

 to the town of Fleetwood-on-Wyre ; both these light-houses liave been pre- 

 viously noticed in the 3rd & 5th volumes of the Journal. The stability of both 

 these light-houses shows with what perfect security many descriptions of work 

 may be placed on siib-marine sand-banks, by means of serew-pijes; especially 

 as Mr. Mitchell proposed for batteries, in consequence of some observations 

 wliich fell incidentally from the Duke of Wellington, when giving evidence 

 before the Shipwreck Committee of the House of Commons. 



His Grace, while speaking on the subject of harbours of refuge, took occa- 

 sion to observe, that the extensive application of steam, to maritime purposes, 

 would effect an important change in naral warfare. That persons on the 

 French coast, the sun being at their back, could see more distinctly what was 

 passing in the channel, than could persons on the English side; which, by 

 enabling steam cruisers to seize upon our merchant ships, at the most de- 

 fenceless points, would, in times of war, seriously affect the trade of London 

 itself; and, on this subject, his Grace concluded by alluding to the possibility 

 of constructing places of defence on the Goodwin Sands, and other banks 

 upon this coast, for the protection of our trade. For the necessity of such 

 works, we have thus the highest military authority. For the purpose of a 

 battery, Mr. Mitchell proposes to renfler his screw-piles available in the fol- 

 lowing manner, for a battery of 28 guns : — It is proposed to support it on 

 foi ty-one malleable iron piles, placed in five parallel rows, the three interior 

 ranges consisting of nine, and the two exterior, of seven piles each, — on the 

 top of these piles an oblong platform is constructed, upon which the battery 

 is formed, with a barrack and alight-house in the centre. 



Among the many advantages to be derived from such places of defence, 

 it may be mentioned the perfect practicability of placing them on sub- 

 marine hanks, adjacent to wide harhours, roadsteads, or estuaries of rivers, 

 such as the Thames, where, from the absence of high and commanding posi- 

 tions, or even dry ground in their neighbourhood, ships of war constitute the 

 only means of defending our trade, in time of war ; the difficulty of which 

 will now be much increased, in consequence of the introduction of steam in 

 the navy. As compared with ships, the risk to such batteries, from hostile 

 attacks, appears trifling; the narrow surface and rounded form of the piles, 

 and each part of the frame-work, rendering it nearly ball proof; for, unless 

 struck in the direct line of the centre, shot would glance off from their curved 

 surface; and, even bar or chain shot could liave no effect on the main sup- 

 ports of the budding, owing to their great strength and weight. 



OBITUARY OF MEMBERS OF THE INSTITUTITION OF CIVIL 

 ENGINEERS.' 



Professor Wallace. 



William Wallace, LL.D., Hon. M. Inst. C. E., late Professor of Matliema- 

 tics in the University of Edinburgh, was born at Dysart, in the county of 

 Fife, in 1768. From birth, fortune, or education, he derived no advantages 

 whatever, and the eminent station he eventually occupied as a mathematician, 

 was achieved solely by his own industry and love of scientific knowledge, 

 aided by natural talents of a high order. He was appointed, at the age of 

 twenty-six, assistant teacher of mathematics in the academy of Perth. In 

 1803 he obtained a piofessorship in the Royal Military College at Great 

 Marlow (afterwards removed to Sandhurst) ; and in 1819, upon the deatli of 

 Mr. I'layfair, and the removal of Mr. Leslie to the chair of Natural Philoso- 

 phy, he was elected professor of mathematics in the University of Edinburgh, 

 llis pursuits and studies were chiefly connected with abstract mathematics, 

 but some of the subjects to which he directed bis attention may be here 

 noticed, as having more immediate reference to the objects of this Institu- 

 tion. 



The Eidograph, an instrument for making reduced copies of drawings, 

 which he invented about the year 1821, and exhibited at a meeting of the 

 Institution in 1839, is considered superior in many respects to the Pento- 

 gragh. It possesses greater smoothness and flexibility of motion, and while 

 the copies may he reduced or enlarged in any proportion, their similarity 

 to the original is preserved with geometrical precision. By a particular 

 modilicafion, the instrument is made not only to reduce, but to reverse the 

 copies, whereby it is rendered peculiarly applicable to the purposes of the 

 engraver. 



.\niong the papers which he contributed to the " Transactions of the Royal 

 Society of Edinburgh," there is one on the subject of curves of equilibration, 

 which is interesting to us on account of its connexion with the theory of 

 suspension bridges. From the development of a certain functional equation, 

 he deduces series for computing the co-ordinates of the catenary, and gives 

 tables of the corresponding values of the co-ordinates so computed ; thus 

 furnishing engineers with a ready means of constructing arches having the 

 forms of equilibrated curves. 



Professor Wallace obtained a high reputation, as a mathematician, at an 

 early age, and during his whole life be laboured assiduously to extend and 

 facilitate the study of his favourite science. Besides his contributions to the 



1 From the Annual Beport of tlie Institnte. 



