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good reasons for establishing the facilities to navigation provided in the act of Congress for this section of the coast, but give collateral information and facts of very considerable interest, adding much to our knowledge of the coast.

In a communication, in reply to questions from the Light-house Board, Lieutenant Commanding McBlair presents the following subjects for consideration : 1. The substitution of a light-house on the ledge called Sow-and-Pigs, off Cuttyhunk, at the entrance to Buzzard's bay, for the light-boat now placed there, and the light-house now existing on the island of Cuttyhunk; (see sketch A.) 2. The placing of a floating beacon on Davis' New South shoal; (see sketch A, No. 2.) This shoal lies near one of the most frequented parts of the ocean, and has occasioned some very disastrous wrecks. It has as litile as eight feet water upon it, is swept by very strong tidal currents, and, during the summer months, is almost constantly hidden by fogs. It was designed at one time to erect a beacon upon it; but the great difficulties of the undertaking, arising from the character of the climate and the distance of the nearest port, seem to be regarded as insuperable. It is, however, indispensable to the safety of passing vessels that it should be marked in as distinct a manner as circumstances will admit. 3. A buoy-boat on the Great Rip, one of the most extensive of the Nantucket shoals. 4. A buoy-boat on the sand shoal lying to the eastward of the northern end of Bass Rip. 5. A spar-buoy on the sand-spit extending from Fox's Point, Nashawena island, at the southern entrance of Quicks' Hole; (see sketch A.) 6. A wooden beacon, (to be painted black,) on Long island, Boston harbor, placed so as to range with the northeast end of Spectacle island, for the safe navigation of the main ship channel; (see sketch A ;) recommended also by Lieutenant Commanding Charles H. Davis, in 1847. 7. A similar beacon on the southeast part of Long island, Boston harbor, to range with Nix's Mate, and to facilitate the passage through the Broad Sound channel. 8. A buoy-boat on the southwest end of Billingsgate shoal, Manchester bay, and two spar-buoys on the southern edge of the shoal, planted at regular intervals between the boat and Billingsgate island. 9. A spar-buoy on Bibb Rock, southward and westward of Wellfleet harbor. 10. Changes in the position of the lights at Chatham, to adapt them to the changes in the coast there.

These recomınendations are fully concurred in, as his field of work has extended, by Lieutenant Commanding Swartwout, who commanded the brig Washington, attached to Lieutenant Commanding McBlair's party.

In connexion with this subject I present the following extract from a report (November, 1850) of Lieutenant Commanding Maffitt, United States navy, assistant in the coast survey:

“I examined a rock in the main ship channel, Boston harbor, near the buoy of the Lower Middle, upon which the British mail steamship Cambria struck, and found it to be identical with a rock already found on the Coast Survey chart to be seen in the work of 1847."

Reconnaissance. It has been necessary merely to extend the reconnaissance in this section, during the present season, to one range of stations beyond the Penobscot, in order to prevent possible interference with the primary triangulation of the next season. This has been done by assistant C. O. Boutelle, and the result is shown on sketch A. The fact that, if necessary to the work, either from the position of the final base of verification in this section or other cause, a point can be found on the Ebeeme mountains readily connected with the coast, has been ascertained. Mr. Boutelle also established the station on Ragged mountain, (Camden mountains.) He was accompanied during his reconnaissance by Major Prince, United States army, assistant in the coast survey.

Mr. Boutelle made, also, a reconnaissance for the main chain of secondary triangles over Casco bay in the course of the season.

Primary triangulation, astronomical observations, 8c.—The party under my immediate charge was transferred to this section in July, and between the second of that month and the fifth of November two stations were occupied for geodetic and astronomical work, and one for astronomical observations. The magnetic variation, dip, and intensity, were measured at two of the stations; vertical angles were measured for height at the three; and a meteorological register was kept during the progress of the other observations. The area of the work, estimated in the usual way, was 2,402 square miles. I was assisted in the measurement of horizontal and vertical angles, and the azimuth determinations, by Lieutenant W. P. Trowbridge, of the corps of engineers, and the observations for time and latitude were made under my immediate direction by sub-assistant George W. Dean.

At Mount Pleasant station, (Oxford county, Maine,) 22 horizontal angles of the primary triangulation were measured by 1,300 observations, with the thirty-inch theodolite of Troughton and Simms, (C. S. No. 1,) 130 vertical angles for difference of height, with the micrometer of this instrument, and thirty for absolute elevation, by a six-inch Gamhey theodolite, (C. S. No. 34,) sets of six repetitions being employed. A signal was placed upon the highest point of Mount Washington, and observed upon whenever the atinosphere was clear.

The azimuths were measured by seventy-two observations, in seven sets, on Polaris, near the upper and lower culmination, the method, referred to in my report of last year, of corresponding azimuths before and after culmination being used. The star was referred to a mark distant about three-quarters of a mile, nearly in a line to the Blue Mountain station, between which and the mark the angle was measured by the micrometer. The observations were made with the thirtyinch theodolite, (C. S. No. 1,) and in five positions of the instrument.

The latitude was determined by Talcoti's method, with a zenith telescope by Würdeman, (C.S. No. 5,) which has been already referred to, having a focal length of forty-nine inches, an aperture of three and a half inches, and used with a magnifying power of six hundred. Two hundred and thirty-six observations were made upon forty-four pairs of stars, arranged from eighty-one stars taken from the Greenwich catalogue; using, also, as many as practicable of the stars of which the places have been determined by the Coast Survey zenith sector. The usual determination of the value of the micrometer and level divisions of the instruinent were made. The longest and shortest sides of the primary triangulation of the season were eighty-four and twenty-two miles, respectively.

Some of the lines from Mount Pleasant having been obstructed by the erection of a new house upon the mountain, a second station point was selected by Mr. Boutelle, about fifty-seven feet from the first, and in the line from Sebattis to the original station. This distance was very carefully measured twice by a standard metre-bar placed on a wooden frame, the two measurements scarcely differing. They were made by myself, assisted by Lieutenant Trowbridge and Mr. Dean.

I was indebted for assistance, in posting heliotropers and other arrangements, to assistant C. O. Boutelle and Mr. Fairfield. Mr. Boutelle also observed for me during a brief absence, on duty, from Mount Pleasant.

At Ossipee station, (York county, Maine,) 15 horizontal angles were measured by 1,470 observations, with theodolite No. 1, and 128 vertical angles for height, with its micrometer, and with the six-inch Gambey theodolite, before referred to.

At Cape Small station, (Lincoln county, Maine,) eleven observations for azimuth were made on seven different days. The observations were made on Polaris-six at upper culmination, four at eastern elongation, and one at western elongation.

The observations for time and latitude, made under my direction by sub-assistant Geo. W. Dean, were as follows:

At Mount Pleasant station, 94 observations for time, upon 16 stars, paired as high and low stars, with transit C. S. No. 6, (Troughton and Simms,)—the equatorial intervals of the wires of this instrument were determined by 47 observations upon six stars. For latitude, 236 observations were made with zenith telescope C. S. No. 5, (Würdeman,) upon 44 sets of stars arranged from 81 different stars selected from the Greenwich twelve-year catalogue. When the places of the stars have been determined with the zenith sector as well as at Greenwich, equal weight has been given to each determination. For the value of the micrometer, 50 observations were made upon Polaris at eastern elongation, and 79 observations upon a collimator for value of level scale.

At Cape Small station, with the same instruments, 104 observations for time were made upon 14 stars, and 243 observations for latitude upon 40 sets arranged from 79 different stars. For the value of the micrometer of the zenith telescope, 91 observations were made upon Polaris at eastern elongation; for value of level of same instrument, 48 observations upon a collimator, in the usual manner.

The time of beginning and end of the solar eclipse of July 27, 1851, were observed at Mount Pleasant station.

The magnetic observations made by sub-assistant Dean, assisted by Mr. Edward Goodfellow, at Mount Pleasant and Cape Small, were as follows: For declination, 132 observations on 9 different days; for horizontal intensity, 7 sets on 7 days; and for dip, 5 sets on 5 days. The declination and intensity were observed with the portable declinometer of Gauss & Weber, as arranged by Professor Lloyd and Colonel Sabine, (Jones, No. 22, C. S. No. 1,) and the dip with a circle of eight inches, belonging to the Smithsonian Institution.

The meteorological observations at these stations, made by Mr. Edward Goodfellow and Mr. B. F. West, consisted of 328 readings for

temperature of the air, for moisture, (wet bulb thermometer.) for pres- sure, (Alexander barometer,) and miscellaneous.

Additional observations were made eight times a day, on eight days, of the barometer, thermometer, &c., by request of Professor Arnold Guyot, of Cambridge, to correspond with his observations for height in the White mountains and the adjacent country. The height of the surface plane, as shown by clouds resting on the Presidents' range, was also noted from Mount Pleasant at his suggestion. These observations were made by Mr. Edward Goodfellow and Mr. B. F. West.

The following magnetic observations were made by assistant J. E. Hilgard, between the 15th and 31st of August. The localities indicate the charts to which the results of the variation will be applied.

Stations. Declination. Dip. Intensity. Bramhall's Hill, in Portland........ 3 days 4 sets 2 sets. Kennebunk Port------------------ 3 * 3 * 2. “ Cape Neddock------------------- 3 * 3 * 2. “

These observations complete the series as far east as Portland harbor. The instruments used were the declinometer No. 20, by Jones, and a nine-inch dip-circle by Barrow, with reading microscopes and verniers. Assistant S. C. Walker has collected, for convenient reference and comparison, all the results obtained by the transportation of chronometers for the differences of longitude of Harvard and Liverpool observatories. The data are those reported by William Cranch Bond, esq., director of the Harvard observatory, for the Coast Survey, and those of the special chronometer expedition of 1849–50, undertaken by the Coast Survey, and under Mr. Bond's immediate direction. They are classified as follows: 1. Results by chronometers making one western voyage, between Boston and Liverpool, and on trial for the government, or for the commercial marine. 2. Results by chronometers used in several western voyages prior to 1849. 3. Results of the western voyages in the special chronometer expedition of 1849–50 (also reported by Professor Bond) with ordinary chronometers. 4. As class 3, but with selected chronometers. 5. Results of eastern voyages, otherwise as class 3. 6. As class 5, but with selected chronometers. The indiscriminate mean of the results by these six classes gives for the longitude of Cambridge, west of Liverpool, 4 hours 44 minutes 39.96 seconds. The services of W. C. Bond, esq., director of the Cambridge observatory, have been rendered to the Coast Survey in various astronomical observations, telegraphic and chronometer operations, the nature and progress of which may be gathered from the following extracts from his report: . “I have to report the observation of thirty moon culminations, a W. of which have been forwarded to the Coast Survey office at ashington, corresponding to similar observations made at Point Pinos and San Diego, California, by Coast Survey assistant Davidson.

- Twelve occultations of stars by the moon and one solar eclipse have been observed at this place, the latter by four observers, each being furnished with separate chronometers and instruments. The telescopes used were of different kinds and powers, according to the suggestion of Mr. Airy, in his paper of instructions relative to this eclipse.

"The results which have been obtained by means of the electromagnetic apparatus for recording astronomical observations are quite satisfactory. This method of adapting the electric current to the wants of the astronomer, and which has grown up under the fostering care of the Coast Survey, is purely American, and is acknowledged as such in Europe.

"The complete apparatus designed and made by ourselves for the coast survey, after having been tested at this observatory during several months, was, with your consent, taken to England, and put in operation, in May last, at the Royal Astronomical Society's rooms in Somerset House, in London, where it was examined and tried by those who felt an interest in such matters, this being considered the most effectual course to pursue in order to convince astronomers of the superior accuracy, expedition, and convenience of this method. At the request of several distinguished scientific gentlemen, the coast survey apparatus was transferred to the rooms of the British Scientific Association, at Ipswich; and, subsequently, we were urged to have it put up in the department assigned to American inventions at the great Exhibition in Hyde Park. As a proof of the estimation in which this is held, I may be allowed to mention that the Astronomer Royal is now engaged in introducing the · American' method of recording into the observatory at Greenwich; and we hear, through the newspapers, that the councilmedal of the great Exhibition has been awarded to our apparatus: it had previously obtained the gold medal of the Massachusetts Mechanical Association. We have nearly completed a similar apparatus for our own use at this observatory, in order more particularly to observe moon culminations, in connexion with your apparatus, when it shall have been put in operation at the Seaton station, in Washington.

“ The chronometer expedition, which you put under my care, for determining the differences of longitude of the observatories of Greenwich, Liverpool, and Cambridge, closed for the season-so far as the transfer of chronometers was concerned-on the arrival of the steamer America, on the 17th instant. We have, this year, the data given for differences of longitude by one hundred and ninety chronometers; these instruments are now on trial for their subsequent rates, and will be subjected, for temperature corrections, to the cold of the approaching winter.

“According to your instructions, I have made preliminary arrangements for the connexion in longitude, by means of the electric telegraph, of the British surveys of the Bay of Fundy and Gulf of St. Lawrence with the United States coast survey. Commander Shortland writes me that he will be in readiness to meet us at Halifax the beginning of November.”

In this section, Wm. Mitchell, esq., has also been engaged in astronomical observations for the use of the coast survey. His results for

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