Imagens das páginas
PDF
ePub

30 000

32. Harbor of Hyannis.....
32. Harbor or Hyannis.............................
33. South side Long Island, No. 1....
34. Hart and City islands and Sachem's Head.
35. Mobile entrance.
36. Chart of Hell Gate.
37. Richmond's Island harbor.....

.......

[merged small][ocr errors]

2. List OF SKETCHES AND PRELIMINARY CHARTS ENGRAVED.

[ocr errors]

doo

30000

0000

........

lo. 1. Sketch chart of Nantucket shoals, (3d edition)...... zoooo 2. ....Do....... Buttermilk channel, New York harbor 5060

....Do.......Cape Hatteras cove............... 20 000 ....Do.......Cape Hatteras inlet............... 20000 ....Do.......Bu

..Bull's Bay harbor ............. ....Do....... Beaufort harbor, North Carolina..... ....Do....... St. Andrew's shoals, Georgia....... 60000 ....Do....... Nantucket shoals, re-engraved and enlarged .............

200'000 9. Hatteras inlet, from re-survey.......

20000 10. Cape Canaveral shoals...... 11. Seacoast Maryland and Delaware .....

200000 12. Hatteras shoals........

120000 13–15. Reconnaissance chart (McArthur's) western coast.

120000 16. Richmond's island ................

20000 17. Sketch chart of Nantucket shoals...... ........ 200000 18–20. Second edition McArthur's chart western coast. 21. Hatteras inlet, re-survey...............

20000 22–26. Five diagram maps Cat Island tides. 27. Reconnaissance of Mosquito inlet.......

40000 28. ... ...Do....... Horn Island pass ......

30 000 29. Sketch of Point Conception........ 30. Sketch of Point Pinos and bay of Monterey.

20000 31. Sketch of Mare Island straits

30 000 32. Current chart Boston harbor. 33. Reconnaissance of Cedar Keys....... 34. ......Do....... Delta of the Mississippi...

::::::.........

300000

60 000 35. ......Do.......Pass Christian ......

τσόστ 36. Preliminary sketch of Galveston bay...

σσσσσσ 37. Sketch of Aransas pass......... 38. Preliminary chart of Trinidad bay....

.. odoo 39. Entrance of the Columbia river......

zooooo 40. Cape Hancock, or Disappointment...... .. OOOO

41. Holmes' Hole. 42–48. Seven maps of progress and geographical positions for

annual report.

[ocr errors]
[ocr errors]

11

3. LIST OF MAPS ENGRAVING.

No. 1. General chart of the coast......

2. No. 1, Long Island sound ......
3. No. 1, Chesapeake bay......

som

lang hindi maganda

[ocr errors]
[ocr errors]

80000

80000

7000

6000

3000

No. 4. Patapsco river......

5. No. 2, south side Long Island.
6. No. 1, eastern series.....
7. Boston harbor........
8. Muskeget channel....
9. Charleston harbor..
10. Key West. .......
11. Connecticut river ....

yoooo 12. No. 2, Mobile bay....

..... totoo 4. LIST OF SKETCHES AND PRELIMINARY CHARTS ENGRAVING. No. 1. Seacoast of Delaware and Maryland; plate enlarged

by electrotyping additional engraving, work of hy-
drographic parties ..

...... Tutor
2. Beaufort harbor...
3. Preliminary chart of Humboldt bay....

3000 4. Preliminary chart of the harbor of Key West Ισσσσσ 5. Sketch of the entrance of the Chesapeake.... Iooooo 6. Re-engraving Nantucket shoals... 7. Chart of the harbor of San Diego. 8. Entrance of San Francisco .......... 9. Savannah river, vicinity of Savannah.. 10. Savannah entrance......

soooo 11. Mobile bay ..................

nooooo 12. Bull's bay, re-engraving.......

.. totoo 13. Entrance to Columbia river ....

.... 1000 14–16. New edition of McArthur's chart western coast.

17. Point Pinos, view.

18. View of mouth of Columbia river. 19–26. Eight maps of progress and geographical positions.

30000

2000T

TTTT

10000

APPENDIX No. 12.

List of geographical positions determined by the United States Coast Surrey.

The present list contains those geographical positions determined by the Coast Survey of the United States which may be supposed to be useful to the navigator, the geographer, and the surveyor. They embrace all the trigonometrical points of the coast survey, determined up to July, 1850, and also positions of a number of prominent objecis determined by means of the plane-table.

For the purposes of the survey, the coast of the United States is divided into eleven sections, in all of which the work is carried on simultaneously. The survey being in different stages of progress in the several sections, and new results being added from year to year to those here given, the same divisions have been adopted in this publication. The several sections are defined as follows:

Sec. I. From Passamaquoddy bay to Point Judith.
Sec. II. From Point Judith to Cape Henlopen.
Sec. III. From Cape Henlopen to Cape Henry.

Sec. IV. From Cape Henry to Cape Fear.
Sec. V. From Cape Fear to the St. Mary's river.
Sec. VI. From the St. Mary's river to St. Joseph's bay.
Sec. VII. From St. Joseph's bay to Mobile bay.
Sec. VIII. From Mobile bay to Vermilion bay.
Sec. IX. From Vermilion bay to the Rio Grande.
Sec. X. Coast of California, San Diego bay, to 42d parallel.
Sec. XI. Coast of Oregon, 420 to 49th parallel.

The tables give the latitudes and longitudes of the trigonometrical points in each section, and their relative azimnuths, or bearings, and distances. The manner in which these data have been obtained may be briefly explained here:

In each section a base line of from five to ten miles in length is measured with all possible accuracy. A series of triangles, deriving the length of their sides from this base, is then established along the coast, by the measurement of the angles between the intervisible stations. In this primary series the triangles are made as large as the nature of the country will permit, because the liability to error increases with the number of triangles.

On the bases furnished by the sides of the primary triangles, a secondary triangulation is next established, extending along the coast, and over the smaller bays and sounds, and determining a large number of points at distances of a few miles apart.

The distances between the points thus determined, as given in the tables, are liable to an average error of about one foot in six miles, until a final adjustment between the base lines shall have been made.

As, on the completion of the primary triangulation in each section, the several series form one connected chain, the different bases afford verifications of each other, and of the triangulation connecting them. The first three sections are thus connected at present.

Observations for latitude and azimuth are made at a number of stations of the primary triangulation in each section. The differences of latitude, longitude, and azimuth between these and other stations are then computed, under the supposition that the earth is a spheroid of revolution of the following diinensions, which are those determined by Bessel from all the measurements made to the present time, viz:

Equatorial radius=6377397.15 metres.
Polar radius =6356079.11 “.

Eccentricity = 0.0816968 It has been found that the differences of lititude and longitude, as computed in this manner from the distance and azimuth between two stations, and which are called geodetic, differ from those obtained by astronomical observations at the several stations, by quantities which are greater than the errors of the observations. Such disagreements are due to local irregularities in the figure and density of the earth, and the error resulting from them in the determinations of latitude and of the meridian plane is designated as station crror. It amounts, according to the results obtained at present, to between one and two seconds of arc in the eastern section of the survey, and to about half a second in the sections south of the Delaware.

In order to eli.ninale the influence of station crrors on the general results, observations are made at a number of stations; the results are referred to a central station by means of the geodetic differences, and the mean of all is used for the computation of the positions given in the tables. The geographical positions inust therefore be considered as liable to future changes, from the accumulation of new observations, and the final discussion of all the results obtained.

The differences of longitude are obtained, as has been stated, by computation, from the distances, latitudes and azimuths of the triangulation. In adding up these differences, from station to station, an accumulation of the unavoidable errors is highly probable. They are checked, however, by differences of longitude, determined by means of the electro-magnetic telegraph, in every section where the introduction of the latter makes it practicable.

SEATON STATION, in Washington city, has been selected as the centre for the telegraphic differences of longitude. The Sections at present connected by telegraph are Sections I, II, III and V. The first three being also connected by triangulation, the check on the geodetic differences of longitude is here obtained, and the agreement is very close.

The longitudes from Greenwich depend upon that of Cambridge observatory, as determined by chronometric differences between Liverpool and Cambridge, and by occultations, eclipses and moon culminations, observed at various observatories in the United States, and referred to Cambridge by means of telegraphic differences. The following statement shows the result up to the present time: Longitude of Cambridge from Greenwich.

h. m. & By moon culminations observed at Cambridge, Hudson,

Ohio, Wilkes' observatory, and National Observatory 4 44 28.4 By eclipses and occultations at Cambridge, Brooklyn,

Philadelphia, and Wilkes' observatory...... .... 4 44 29.6 By chronometric differences....................... 4 44 30.1

The longitude adopted for the present is 4h. 44m. 29.5s., or 71° 07' 22.50.

In Sections IV, VI, VIII, IX, and X, the longitudes are counted from some central station in each. Sections IV and VIII will soon be connected by telegraph with Seaton station and Cambridge. In Sections VI and IX the longitudes from Greenwich will for some time depend upon less exact determinations. For the present we have the following data: Sec. IV. Stevenson's Point, west of Greenwich......... 76 10 43.5 Sec. VI. Cape Florida..........ditto....... .. SO 05 00 o " Sand key.............ditto...

.....ditto...............*81 52 43 Secs. VIII and IX. Fort Morgan, Mobile Point......... 88 00 25 Sec. X. Coast Survey observatory, near San Diego....*117 13 22

Explanation of the tables. The first column on the left contains the name of the several stations or triangulation points. Their general locality is indicated by the

* Corrected from data to November, 1852.

heading at the top of the page, by means of which they will be readily found on the sketches accompanying the tables. Sub-headings in the first column indicate the locality more minutely where it is practicable. The stations are generally either prominent objects of permanence, such as spires, light-houses, beacons, &c., or they are the points on E. hills, capes, or points of land, where signals have been erected or the purpose of the survey, and which are marked on the ground. In a small number of cases in the first three Sections, but much more frequently in the southern Sections, where settlements on the coast are sparse, and few permanent objects are to be found, the stations have no other distinguishing mark than the signal erected on the spot; and after its decay, the mark left on the ground, to designate the station point. The latter generally consists of posts or stones set around the point, while the centre of the station is Wood by an earthen cone or glass bottle buried under the surface of the ground and marked on top by a stone or post. Where the station is on a rock, a copper bolt, or a hole filled with lead or sulphur, will be found to designate the exact spot. The sketches showing the configuration of the land, as well as the relative positions of the stations, no great difficulty will be experienced in finding the latter, when desired for local surveys or reference. In any case where minute descriptions of particular points are required, they can be had by application addressed to the Coast Survey office. The second and third columns contain the latitudes and longitudes of the stations named. The fourth column contains the azimuth of the line joining the station named in the first column to that named in the fifth; that is to say, the angle which that line makes with the meridian of the former station, reckoned from south around by west, through the whole circle. The sixth column gives the back azimuth of the same line, or the angle which it makes with the meridian of the latter station, reckoned as before; the difference between the azimuths in the fourth and those in the sixth columns being 180°, less the inclination of the meridians at the two stations. The seventh, eighth, and ninth columns give the distances, in metres, yards, and miles, between the stations named in the first and fifth columns. The relation of the metre to the yard used in obtaining these results, is— 1 metre+1.0935696 yard, or 39.36850 United States standard inches.

For each station the azimuths and distances to two other stations are given. In every case the lines so given have actually been observed.

In each section the stations of the primary triangulation are given in a separate table, in which all the distances and azimuths observed are given. Whenever these primary stations afterwards occur in the columns of the general table, they are distinguished by being printed in small capitals.

Those points which are marked with an asterisk have been determined by means of the plane-table; their positions are not as accurate as those of the trigonometrical points, and are liable to be in error about three metres, or ten feet.

« AnteriorContinuar »