« ForrigeFortsett »
“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 Exbibition 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 the year consist of 200 pairs of zenith distances of stars, 37 moon culminating observations, 2 occultations, and 50 meridian transits for time.
Secondary triangulation. The scheme of secondary triangulation of the coast of New Hampshire and part of Maine, between the Piscataqua and Saco rivers, commenced last year by Captain T. J. Cram, United States topographical engineers, assistant in the coast survey, has been completed this season to the line Ossipee-Fletcher's neck, (see sketch A,) including its complete connexion with the primary work. The party took the field on the 20th of June, between which date and the 7th of October, to which Captain Cram's report extends, 20 stations were occupied, and 952 sets of observations made on 199 points, consisting of stations, light-houses, steeples, &c, with the twelve-inch repeating theodolite of Troughton & Simms, (C. S. No. 18.) Of these stations occupied, eight were in New Hampshire and twelve in Maine. Not less than six repetitions with the telescope direct, and six telescope reversed, were counted as a set; the total number of observations being 8,148. The area covered by the secondary triangulation proper, and including the triangles which connect it with the primary work, is 700 square miles.
At the station marked “ Mason” on the sketch, the instrument was elevated fifty-two feet above the ground, to avoid expensive cutting of the woods around it. Captain Cram reports the results of this experiment to be satisfactory.
This work is connected with the secondary triangulation of the coast of Massachusetts, by assistant C. O. Boutelle, on the southwest, at the line " Powow-Seabrook;" with the secondary triangulation laid out for Casco bay, by the same assistant, on the line" Fletcher's neck-Ossipee:" it unites with the triangulation of Portsmouth harbor, by Captain Stansbury, United States topographical engineers, on the line “NewcastlePulpit rock," and is controlled by the connexion with the primary stations “Pattuccawa," " Agamenticus,” and “Ossipee," and the stations “ Isle of shoals” and “Fletcher's neck,” observed upon in the primary series. In all the connexions referred to, the importance of which is ably set forth in Captain Cram's report, there are lines of verification.
Captain Cram was engaged during the winter in copying in duplicate and in computing his work of the past season, as far as the data were complete; the entire office work was not, however, finished, before it was necessary to take the field; so that with the completion of the scheme of triangulation of this part of the coast this year, there is a considerable accumulation of office-work.
After the date of my report of last year, assistant C. 0. Boutelle completed his work connecting the secondary triangulation of the coast of Massachusetts with that of New Hampshire and Maine, erecting the necessary signals and measuring the angles, between the 1st of Octo ber and 8th of November. The number of stations occupied was 12, and 156 angles were measured, upon 154 objects, by 950 observations. Vertical angles were also measured upon 38 objects, 59 zenith distances being determined by 578 observations. The instrument used in both cases was an eight-inch theodolite by Gambey, (C. S. No. 24.) In
reference to the method of determining heights by observing zenith distances, Mr. Boutelle remarks:
« The height above the mean level of the sea of the point of observation, in the tower of the Harris street church, (Newburyport,) has been carefully determined. The plane of mean level of the sea was obtained by observations on seven consecutive tides in the Merrimack river, at one of the Newburyport wharves. These were referred to a bench-mark on the top of the wharf, from whence a series of levels was carried to the church. It is pleasant to be able to state that the height of • Powow hill,' determined from these observations, differed less than a foot from that obtained by a series of zenith distances, running through many sides of triangles, from levels taken at Dorchester Heights and Nantasket, in Boston harbor."
Mr. Boutelle was assisted by Messrs. Fairfield and Gregorie. After closing this work, he proceeded to the office to prepare for the duty assigned him in Section V, of which an account is given in its proper place.
Topography.—The topography has employed two double parties and one single party during the chief part of the season: one of the former working on Cape Cod, the other on Cape Ann, and the latter near Newburyport. The plane-table sheets are shown on sketch A, and are numbered 28, 311, 37, 38, 39, and 41. The area embraced in them is 66 square miles, and the extent of shore-line 217 miles.
The weather, which has been generally unfavorable for the operations of the survey, has been very favorable to the execution of the topography. The nature of the ground in this section makes it, however, the most difficult to represent, from its varied surface, and from the number of details required in many places by the closely settled character of the country,
A double party (that is, a party working two plane tables) under the charge of assistant H. L. Whiting, with Mr. R. M. Bache as assistant, has been occupied from the latter part of June until early in October, in continuing the topographical survey of Cape Ann. The work is comprised in three sheets, Nos. 37, 38, and 39, (sketch A,) and extends from Beverly farms, near Salem, along the south shore of the cape to its extremity; and on the eastern shore to Halibut Point, the northeastern point of the cape. The area embraced is 35 square miles, the extent of shore-line 60 miles, and the extent of coast measured, in its general direction, about 18 miles. The topography includes Manchester and Gloucester harbors, and Rockport, and extends from the shore to the nearest road in the interior, thus including nearly all the area between the water-line and the rocky and wooded portion of Cape Ann, until near the eastern portion, when it embraces the highest ground of the cape. The difficult character of this survey will be understood from Mr. Whiting's general description of the topography of the cape: “The character of the country is broken and rocky. The range of hills forming the back-bone, as it were, of the cape, is covered with a mixed growth of pine, oak, maple, &c., and is generally unsusceptible of cultivation; the land is sterile, and among the valleys and broken ridges are numerous swamps. The average height of the hills
and ridges is from 150 to 200 feet, with occasional peaks of 225 and 230 feet.
• The extremity of Cape Ann, including the townships of Gloucester and Rockport, is nearly an island, formed by the inlet of Gloucester harbor and river from the south, and Annis Squam harbor and river from the north. These waters nearly unite; and formerly a canal was opened, making a communication between them; but the tide meeting from the two entrances and the shoal waters of Squam river made it of little service; and now the main road to the peninsula is diked across the canal, entirely closing it.
“ The interior of the peninsula is lightly wooded among the hills and swamps, but generally barren of foliage. The land first seen from sea is · Poole's hill,' about 230 feet high. Pigeon hill is about 195 feet; but being quite near the shore, is soon made from sea. Rail-cut hill is about 210 feet, and near Gloucester harbor.
“ The character of the shore and waters of Cape Ann is more bold and broken than any thus far surveyed in this section.”
The shores of the extremity of Cape Ann are bold and abrupt. “Coasting vessels, in rounding the cape, pass quite near the shore; and the harbor of Gloucester is quite deep in comparison with similar waters to the westward.
6. There are some dangerous ledges and rocks off the eastern point of the cape, the • Salvages,' the · Londoner,' &c.; but the lights of Thatcher's island are sufficient guides to navigators in avoiding them, and I believe but few wrecks or disasters occur to vessels in passing the cape.
“ The character of the topography has been of the most complicated and intricate kind, the details in contour, outline of shore, &c., being the greatest yet surveyed in this section. The artificial details in the towns of Manchester, Gloucester, and Rockport, are also very great."
The work in Beaufort harbor, North Carolina, by Mr. Whiting, is described under the head of Section IV; he is now under instructions to proceed to Savannah river, (Section V.)
A double party, under charge of assistant J. B. Glück, with Mr. W. S. Walker as aid, was at work on Cape Cod from the latter part of July to the close of October; at first on the sheet No. 28, in the vicinity of Chatham, and next on No. 31), near Welfleet. Up to the first of October, the area surveyed was eleven and five-eighths square miles, and the extent of shore-line 72 miles. In his report, Mr. Glück remarks: “In illustration of the intricate nature of topography upon sheet No. 28, Cape Cod, I would state here, that an area of only 71 square miles contains not less than 162 hill-tops, 143 hollows, and 21 ponds of larger and smaller size, with hills from 10 to 100 feet high, the representation of which forms a most complicated system of horizontal curves; a circumstance which should explain satisfactorily the comparatively small amount of area surveyed upon Cape Cod.” The shore-line of Chatham harbor was furnished to the hydrographic party who made the examination there.
On the Welfleet sheet, (No. 311,) Mr. Glück surveyed 54 square miles, and determined 18 miles of shore-line, closing his work in this section, and transferring his party to the Patapsco (Section III) at the close of October.
The surveying done by Mr. Glück in Sections II (for light-houses in New York harbor) and III (Patapsco river,) will be found noticed in its appropriate place.
Assistant A. W. Longfellow commenced the execution of the topography of Newburyport harbor on the 15th of August, and will discharge his party about the 20th of November. Up to the 1st of November he has surveyed an area of 13} square miles, and an extent of shoreline of 67 miles. The work was begun on Plumb island, and included, * first, the immediate shore-line of the harbor and approaches, which were furnished at once to the sounding party, for use in their operations. It includes the wharves and principal streets of the city, and will com ise, this season, all that is necessary for a harbor map. The plane-table sheet of this work is numbered 41 on the sketch A.
Hydrography.—The party under the command of Lieutenant Charles H. McBlair, United States navy, assistant in the coast survey, commenced work about the close of June, and finished about the middle of October. (See sketch A, Nos. 1 and 2.) The continuation of the hydrography of Nantucket shoals formed the first object of the season; next, the completion of the work in Muskeget channel, for the chart of that passage, which is nearly prepared for publication; next, some supplementary work between Martha's Vineyard and Block island, for the off-shore chart, which is also nearly engraved; and last, the completion of the hydrography of Salem harbor. The progress made, to September 25, is stated by Lieutenant Commanding McBlair in his annual report, as follows:
“The hydrography of the shoals was prosecuted between the 3d July and sih September; that of the Muskeget channel, between the 9th and 13th of September; and the remaining period, between the last date and the present time, has been occupied in the filling-in work to the westward of Martha's Vineyard.
“ The results obtained in the different sections are exhibited in the annexed tables. (See sketch A, Nos. 1 and 2.)
1. Field of work.- Nantucket Shoals.
Area included within sounding limits ........... 130 square miles. Extent of sounding lines...
.. 252 miles. Number of casts of lead.......
..... 2,622 Depth of water ................varying from 13 feet to 23 fathoms.
2. Field of work.—Muskeget channel and approaches.
Area within sounding limits.....
...... 43 square miles. Extent of sounding lines ...... .......... 103 miles. Number of casts of lead ......
........2,956 Depth of water ..... ....varying from 6 feet to 21 fathoms,