Imagens das páginas

length only one-third of a mile across the shoal, running NE. and SW.

“Two large iron buoys, properly marked, placed, and moored with heavy moorings, or with Mitchell's screw, would render this channel one of great value, not only to the local trade of the Cape Fear region, but to the coasting trade in general, along the southern coast.

"Any vessel capable of crossing either bar at the mouth of the Cape Fear river, would find no difficulty in crossing these shoals under ordinary circumstances of weather and sea, when these channels shall have been properly marked out by large buoys, enabling those threatened by bad weather to make a port under almost every condition of weather.

“Too much importance, it is believed, cannot be attached to the subject of marking, as perfectly as may be possible, the channels over these dangerous shoals, for the benefit of the coasting trade, and of furnishing means by which to guide the navigator bound north or south in passing outside of them.

* Two large iron buoys are required to mark the best channel over these shoals for coasters.

“ The present light-house at Bald Head (said to have an elevation of one hundred and ten feet above the level of the sea) is inadequate as a seacoast light to the wants of the mariner. It is of comparatively little use now, owing to two causes: its great inferiority in brilliancy and intensity, and its bad location, being three and one-third nautical miles from the point of the cape.

“ The outer part of the shoals is twenty nautical miles from the lighthouse, and seventeen from the pitch of the cape.

" Assuming that the present light can be seen as far as the curvature of the earth will perinit, (which is not the case,) from the deck of an ordinary merchant vessel, the range in good weather will be fifteen nautical miles-five nautical miles short of the required range to reach the extremity of the shoals.

“To render a light efficient here, it will be necessary to change the location to a position as near the end of the cape as safety and prudence will permit; give the tower an elevation of not less than one hundred and fifty feet, and place in it a first-order dioptriv apparatus, combining all the most recent improvements.

“An elevation of one hundred and fifty feet will give an ordinary range from the deck of a merchant vessel of nineteen to twenty nautical miles, leaving the mariner two or three miles on the safe side of the dangers.

“At present the fleets of vessels passing daily these dangerous shoals have nothing but the lead to guide them around them, while contending with currents, which are to a great extent, if not wholly, influenced in strength and direction by the winds.

“The removal of the present Bald Head light-house would work no disadvantage, as it is too far inland for a seacoast light, especially with its present apparatus; and is of very little, if of any, use in a local point of view.

“Until the present light-tower can be removed to its proper location, and a first-order lens apparatus be procured for it, a large light-vessel ought to be built and placed in the slue, at the distance of fourteen nautical miles from the present light-house. If this vessel is fitted with proper parabolic reflectors and argand burners, and distinguished in a manner to prevent mistakes, it will contribute greatly to the security of life and property, and enable navigators, bound either north or south by this point, to shorten their passage by running boldly, when now they are compelled to creep along with the lead constantly going.”

Light-houses, beacons, buoys, fc.— The providing and placing the bellbeacon and iron-buoy, off Cape Hatteras, having been intrusted, by the Secretary of the Treasury, to the Coast Survey, a contract has been made for them to be delivered in the spring of 1852, the earliest period at which it was deemed safe to place them.

In the Appendix (No. 29) will be found a report upon the subject of lights and buoys for Beaufort harbor, North Carolina; also, in the Appendix, (No. 30,) a report upon the necessity for a light-house on the Upper Jettee, Cape Fear river, North Carolina. In regard to the former, Lieutenant Commanding Maffitt observes, that if the lights and buoys be placed as recommended, vessels will enter the harbor in safety, by day or night, without a pilot.

The suggestions of Lieutenant Commanding Jenkins, United States navy, assistant in the coast survey, in reference to lights and buoys in the vicinity of Hatteras shoals, have just been given in full under the head of hydrography.



In this section two parties have been in the field engaged in triangulation and two in topography, besides the party employed upon the - hydrography. The operations have been as follows:

1. Astronomical observations at Savannah, and the preliminary triangulation of the entrance to Savannah river. (See sketch E, No. 2.)

2. The connexion of Charleston and Savannah for difference of longitude by telegraph.

3. The triangulation of North Edisto river, South Carolina. (Sketch E, No. 3.)

4. Secondary triangulation of St. Helena sound and the South Edisto and Ashepoo rivers, extending from Edisto island on the north to the Hunting islands on the south, coast of South Carolina. (Sketch E,

[ocr errors]

and har bopletion of the part o

5. A topographical survey of North Edisto river. (Sketch E, No. 3.) 6. A similar survey of part of Savannah river. (Sketch E, No. 2.)

7. Completion of the hydrography of Charleston bar, approaches, and harbor. (Sketch E.)

8. Hydrographic reconnaissance of Savannah river and bar. (See sketch E, Nos. 4 and 5.)

9. Hydrography of North Edisto bar and river. (Sketch E, No. 7.) 10. Tidal observations day and night at several stations.

A map of Charleston harbor, on a large scale, has been engraved, and will be published at once.

" Front”aand nearly rea of South Carosee sketch

A chart of Savannah bar and another of the harbor, with the “Main," “Front” and “Back” rivers, have been furnished to the office, and are engraved and nearly ready for publication. The plate of the chart of Bull's bay, on the coast of South Carolina, northeast of Charleston harbor, is in process of re-engraving. (See sketch E, No. 6.)

The chart of North Edisto river and harbor of refuge is put in hand for engraving, and will be published as early as practicable.

At the request of the Chamber of Commerce of Charleston, and by authority of the Treasury Department, a copy of the Charleston harbor map, on a large scale, has been executed, and will speedily be surnished to that body. (See Appendix, No. 30 bis, for correspondence.)

After a fair trial in this section, it has been found expedient to cause the secondary, and in some cases the tertiary, triangulation to precede the primary. The greatest difficulty in the primary work is the preliminary tracing, through woods and swamps, and the cutting. The secondary and tertiary work following the circuitous course of the streams, and availing itself everywhere of continuous natural or artificial openings, affords means of running the primary lines from point to point with approximate accuracy, and of correcting readily any errors which occur in running. In executing this triangulation on and near Edisto island, and along the rivers which intersect it, parts of the base of the primary triangulation, which had been marked in the measurement, have been used, as convenience suggested, for the bases of the secondary work.

The difference of longitude of Charleston and Savannah was determined by telegraph, the line having been kindly placed at our disposal, after business hours, by the president of the company, Elain Alexander, esq. At the Charleston end the observations were made by Professor Lewis R. Gibbes, at his observatory; and at the Savannah end by assistant C. 0. Boutelle. This connects the Seaton station at Washington with Savannah, the difference of longitude of Charleston and Washington having been determined in our operations of the previous year.

A full report of the computations of the observations by which the difference of longitude was obtained, between Professor Gibbes' observatory, in Charleston, and the Seaton station, at Washington, has been made by assistant S. C. Walker. The mean result is, Charleston west of Washington 11m. 45.27s., with a probable error of + 0.02s.

In April last I visited the parties in this section for the inspection of their work, and to arrange the details of instructions to the topographical and hydrographic parties in Savannah river. The work was obviously advancing very satisfactorily, and the difficulties which attended its beginning were giving way before the increased experience of those engaged.

The kindness received from the gentlemen near whose residences the operations of the parties bring them, and the facilities uniformly extended in the execution of the work, in many cases at a considerable sacrifice of personal convenience, are acknowledged by all the parties in their reports. As a public acknowledgment by name might be deemed intrusive, I take this method of returning the best thanks of those employed in this section of the survey.

Astronomical Observations.—The observations for time, latitude, azimuth, and difference of longitude from Charleston, at the Exchange of Savannah, were made by assistant C.O. Boutelle, aided by Lieutenant Joseph S. Totten, United States army, detailed for coast survey service; and during a brief period by Professor E. Yulee. An astronomical clock by Kessels had been converted by Mr. Saxton into a circuit breaker, and was used for the observations of local time and for transmission of telegraphic time signals to Charleston. The transits of sixty-five stars were of: to Charleston, and of fifty-eight were received from thence. They were usually observed on all the twenty-five wires of the diaphragm, and all were recorded on the Morse registering fillet. Two hundred and forty transits of sixty-five stars were observed for local time and deviation. The transit instrument was one of those of forty-five inches focal length, by Troughton & Simms, (C. S. No. 4.) with a diaphragm of twenty-five wires, by Würdeman, of Washington. The observations for latitude were made with a new zenith telescope by William Würdeman, of Washington, (C. S. No. 5,) which is spoken of in terms of commendation by Mr. Boutelle. Seven hundred and forty-six observations were made on one hundred and twenty-six stars, paired according to Talcott's method. The values of the micrometer and level scales were duly determined, the former by observations on Polaris at elongation, a method first proposed and used by Mr. Boutelle. The azimuth observations were made, by the kind permission of the mayor of the city, from the cupola of the Exchange. The instrument used was a twelve-inch theodolite by Gambey, (C. S. No. 30.) The results are recommended by Mr. Boutelle for adoption in the secondary triangulation only. Professor Lewis R. Gibbes has observed at the Charleston observatory during the past year, for the coast survey, 39 moon culminations, and 95 transits of moon culminating stars, and six occultations. In connexion with these, 54 observations have been made, with reversal, on circumpolar stars, and on 130 zenith and equatorial stars, for time and instrumental corrections. In the telegraph operations for longitude, 52 stars were telegraphed on 1,220 wires. The importance of keeping up the observations at various points, so as to be sure of corresponding observations with those on the western coast, for longitude, is very great. It secures a clear night for observing, at some one point, when the positions are scattered over a considerable range of country. Primary triangulation, and secondary connected with it.—The operations were under the charge of assistant C. O. Boutelle, aided, during part of the season, by Lieutenant Joseph S. Totten, United States army, and during nearly the entire season by J. W. Gregorie, esq. They were commenced by the triangulation of the North Edisto river, (see sketch E, No. 3,) in which nine stations were occupied, and 104 angles measured, on 86 objects, by 785 observations with an eight-inch Gambey theodolite, (C. S. No. 2.) The services of Mr. Boutelle being required at Savannah, this triangulation was completed by Mr. J. W. Gregorie, who retraced and opened several lines, and erected signals for the primary triangulation. In March, Lieutenant Joseph S. Totten made a reconnaissance for the triangulation from the Edisto to the Stono river, inside of, and parallel to, the sea-beach. The reconnaissance made by Mr. Gregorie up the Dawho to Aiken's station on Jehossee, and along the Wadmelaw river to New Cut, is shown upon the sketch-(sketch E, No. 3.) Mr. Boutelle remarks: “I make it a point to avoid extensive cutting in secondary triangulation, and it is a matter of much difficulty to get triangles of proper form without it. The houses along the river aid us much in carrying out our schemes of triangulation; and I cannot too often express the obligation we are under, for the uniformly friendly and courteous manner in which our requests to be allowed to erect signals and place instruments upon them are complied with.”

Two primary stations, viz: the east and west ends of the base, were occupied by Mr. Boutelle for the measurement of horizontal angles, and at one (east end of the base) azimuths were measured. The observations were made with a theodolite by Würdeman, (C. S. No. 30.) It was found absolutely necessary to employ heliotropes in order to obtain a sufficient number of observations without a long delay.

In the entire work, of both classes, executed by this party, from taking the field in December to the close of the season in May, 15 stations were occupied, and 173 angles measured, on 158 objects, by 2,073 observations. This is in addition to the astronomical determination at Savannah, already noticed. The work was continued as long as the means provided for this particular party permitted.

An examination for points of triangulation for the entrance to Savannah river, to be used by the hydrographic party in sounding out Tybee bar, was made by assistant Boutelle in March, and it was intended that he should execute this operation personally; but having been temporarily disabled from work by an accident occurring after his pariy at Edişto had been discharged, the triangulation was made under his direction by Mr. J. W. Gregorie. The preliminary work intended for immediate use in a hydrographic reconnaissance is shown on sketch E. Twelve stations were occupied, and 218 angles measured, on 33 objects, by 383 observations. The operation was closed on the 3d of June.

The results of the triangulation of North Edisto river were furnished to the topographical party surveying those shores, and those of the Savannah river to the hydrographic party sounding the entrance and harbor.

The great activity of the party under Mr. Boutelle in field-work has involved a corresponding amount of office-work, in which he has, except during brief intervals of field duty which have been elsewhere stated, been laboriously engaged. In these computations he has been assisted by Messrs. G. A. Fairfield and J. R. Offey. Lieutenant J. S. Totten was, on the closing of the field-work in this section, attached to the party of assistant Edmund Blunt in Section III, (Virginia,) and Mr. J. W. Gregorie to that of assistant Bolles in Section IV, (North Carolina.)

Secondary triangulation.—The secondary triangulation executed by assistant Charles P. Bolles is shown in sketch E, No. 3. It rests upon a portion of the base on Edisto island measured for the primary work, and, gradually widening out, covers the South Edisto and Ashepoo rivers, and St. Helena sound, furnishing a very well conditioned scheme of work, and well selected points for the use of a topographical party,

« AnteriorContinuar »