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LIGHTHOUSE ON THE NEW SOUTH SHOaL, NANl'tfCKET, t. S. 



[i§55. 



ticularly in periodicals devoted to such and kindred subjects ; 

 but as these, in consequence of the restrictions upon the pur- 

 chase of books, are only occasionally accessable, and then 

 through private sources, nothing is positively known as to 

 the fact. 



The objection to screw-piles for founding a work at New 

 South Shoal does not apply— ^except as to giving them their 

 true relative position — to pneumatic piles, which, being sunk 

 into the bottom by atmospheric pressure caused by exhausting 

 the air from the hollow shaft, the erection of a fixed structure, 

 such as that required to apply the mechanical power to drive 

 the former, is dispensed with, and the objection to the great 

 length of the pile through which this power must be exerted, 

 at the same time got rid of- But it must nor. be supposed, 

 that because a fixed structure is not indispensable, a floating 

 body is deemed sufficient for the successful application of atmos- 

 pheric piles in the present instance. This is not the case. 

 That these piles may be planted singly in favourable weather 

 at so exposed a point as New South Shoal, by well-devised 

 measures fully matured, from so unstable a footing as a floating- 

 body, the sinking of the cylinder on the Goodwin Sands is of 

 itself abundantly sufficient to prove; but that the number of 

 piles required to constitute a foundation for a liglit-house or 

 beacon i^iay, under the circumstances, be made to receive their 

 proper relative positions, so far at least, as to render them pro- 

 perly available for the intended purpose, is not believed. The 

 manner in which it is proposed to provide against this objection 

 in the use of the atmospheric pile in the present case, or at 

 othef points of equal exposure, will be explained in the project 

 now submitted. 



Having premised that tbougli a solid structure at New 

 South Shoal, were it possible to erect one at that exposed 

 point, might withstand the direct assaults of the sea, it never- 

 theless would be overthrown by the wasting of the sands on 

 which it stands, through the insidious workings of the waves 

 acting on the mass, and that to meet the case, it would be 

 necessary to adopt a foundation ; which, while it afforded the 

 necessary area and strength to support the required superstruc- 

 ture, would off'er no impediment, practically considered, to the 

 motion of the currents or the waves ; having also expressed 

 the opinion that works combining these pre-requisites may be 

 founded on submerged soils by means of Mitchell's screw-pile 

 ahd Pott's pneumatic-pile— and further, that for reasons which 

 it is conceived are indisputable, the former cannot be applied 

 to that use at New South Shoal — the bureau will already be 

 prepared to learn that, as the practical application of the latter 

 is not open to the same objections, it is recommended for the 

 present design. 



The instructions of the bureau calling for a plan and 

 estimate for a beacon on New South Shoal are pi'edicated on so 

 much of the " Act making appropriations for light-houses, 

 light-boats, buoys," &c., approved March 3, 184-9, as is con- 

 tained in the following words, to wit : " For a screw-pile 

 beacon or other practicable structure on New South Shoal, off" 

 Nantucket, discovered by the survey of the coast, 825,000, to 

 be expended under the direction of the Bureau of Topogra- 

 phical Engineers." A plan and estimate for a beacon are 

 accordingly herewith submitted. Considering, however, that a 

 beacon would mark the shoal during the day only, and that the 

 risks and dangers of navigation are more imminent and numer- 

 ous at night, and especially during the boisterous season, when 

 the nights are longest, it has been deemed advisable, in antici- 

 pation of the approval of the bureau, to prepare also a plan and 



estimate for a light-house for the same point. In doing this, 

 less hesitation has been felt, because, in the erection of any 

 work at a position so exposed as the one under consideration, 

 the only real difficulty consists in establishing the foundation ; 

 and because the greater cost of a lighthouse, although certainly 

 considerably more than for a beacon, bears no sort of reasona- 

 ble comparison when the superior and continuous usefulness of 

 the lighthouse is considered. It was also conceived that the 

 plan might be so arranged, that in case the beacon structure 

 should be adopted, and should, when raised, be found com- 

 petent to resist the shocks of the ocean, the project of a light" 

 house might be finally executed. In contemplation, therefore, 

 of that ultimate object, the dimensions of the proposed beacon, 

 in general and in detail, have been enlarged beyond what might 

 be otherwise considered sufficient; but whatever maybe the 

 excess thus caused in the estimate for the beacon, it is confined 

 almost wholly to the foundry cost of the structure. In other 

 respects, unless the size of the work should be greatly reduced, 

 the expenses, excepting those in which time enters, would 

 remain nearly, if not quite, the same. 



As the two structures, as already stated, are in part commoS 

 to each other, a description of the lighthouse, as the larger of 

 the two, will, with occasional reference to the beacon, be suffi- 

 cient for both. 



The foundation is composed of iron piles, so grouped together 

 as to form an octagonal prism 50 feet in diameter, and about 

 42 feet in height. From this prism, as a base, rises a trun- 

 cated pyramid, composed also of iron piles, which inclining 

 inward 6 on 1, for a further height of 120 feet, fall within the 

 diameter of 10 feet, and are received and secured in a great 

 ring-piece, which, in turn, is surmounted by the watch-room 

 and lantern, making the whole height 185 feet. The piles, 

 one at each angle, and one at the centre of the octagonal prism, 

 are of 12 inches ; those of the truncated pyramid in three 

 lengths of 12 inches, tapering to 6 inches. The entire structure 

 including the prism for the length of the piles, is braced hori- 

 zontally in seven planes, and diagonally between every conse- 

 cutive twq of these planes, except where the dwelling of the 

 light or cage of the beacon, as the case may be, interferes, 

 when these are in part omitted. The dwelling stands 40 feet 

 above the highest tides, is composed of three stories of nine feet 

 each, and communicates with the watch-room and lantern 

 above by a spiral stairway in a column of wrought-iron 8 feet 

 in diameter. The two lower stories are 30 feet, and the upper 

 story 20 feet in diameter ; the first and third stoi-ies, as well as 

 the roof of the dwelling, and the watch-room and lantern being 

 surrounded by galleries. The wiitch-room and the lantern are 

 12 feet in diameter; the former 6 ft. 9 in. in height, the latter 

 about 12 feet, with the roof and ventilator, &c., 20 feet in 

 height. The beacon occupies but two of the three lengths of 

 piles forming the pyramidal frustrum of the larger structure. 

 The cage, the bottom of which is elevated 60 feet, and the 

 extreme top 108 feet above the level of the highest water, is 

 composed of columns arranged in the form of a cylinder, 24 

 feiit in diameter and 24 feet in height, surmounted by a canopy 

 giving it a further height of 24 feet. 



These are the outline or main features of the two structures. 

 The details will be better understood from the drawings com- 

 municated herewith, than from the most lengthened and 

 minute description. They consist of an elevation and vertical 

 section of each work on a scale of 4 feet to an inch (1-48), 

 and sixteen sheets of details on the same, and double 

 the scale; and will show, not only the manner of bracing pro- 



