« AnteriorContinuar »
harbor, and that it should be constructed with sufficient stability to resist the ice when it breaks up in the spring.
The two beacons to be placed near Fort Hamilton are important: they should be placed upon the continuation of the sailing line, as represented on the Coast Survey chart, from near southwest spit up mid channel, to serve as leading marks by night as well as by day. The southern beacon should be placed near the fish-house, and the northern one near the rekloubt. It is believed that a proper position may be found for the northern one on the public land, without interfering with other interests. One keeper could attend to these two beacons, provided his dwelling is placed contiguous to them. (See Coast Survey chart accompanying this report.)
A fog-bell is necessary for the Newark light-house.
A buoy on Mill Rock, (Constable's Point,) and four buoys to mark the channel of the Passaic, have been found already placed. The accompanying Coast Survey chart will exhibit the approximate positions of the buoys. The can-buoy on this sketch is a short distance to the eastward of the position for the beacon authorized to be erected, which we consider to be important, and recommend that it be built on three wooden piles, driven at the angles of a triangle, with the proper inclination to form a pyramidical structure when boarded up.
We recommend that the buoy now occupying the position of the beacon may be placed on the three-feet sand-knoll, to the southward and eastward of the Newark light, when the beacon shall be completed.
The proposed beacon to be placed at the corner stake, near Elizabethtown Point, is an important and very necessary aid to navigation. We recommend that it should be built in the same manner described for the one at the mouth of the Passaic.
The piles for this and the Passaic beacon should be coppered a sufficient distance above and below the water, to prevent the ice from injuring them; any solid structure would injure the channels.
Very respectfully, yours,
THORNTON A. JENKINS, Lieutenant U. S. Navy, Assistant U. S. Coast Surrey.
Lieut. Com. U. S. Navy, Assistant Coast Survey. Prof. A. D. BACHE,
Superintendent U. 8. Coast Survey.
APPENDIX No. 25.
Report of Sears C. Walker, assistant in the coast surtey, communicating the
measures of wade-time made from 1849 to 1851.
CAMBRIDGE, September 30, 1851. DEAR SIR: I beg to submit a statement of the experience of the Coast Survey on the subject of galvanic wave-time, since my last annual report of October 15th, 1850.
The result of our experience was then stated, as follows:
1. That the average of all our experiments to that time indicates a velocity of propagation of the inducing waves of 15,400 miles per second in the iron wires of a telegraph line.
2. That the velocity of propagation through the ground appears to be less than two-thirds of the volocity in the iron wires.
These conclusions were in accordance with the independent results of the researches of Dr. B. A. Gould and Mr. Karl Culman, previously read, and since published in the proceedings of the American Association for the Advancement of Science, at their meeting at New Haven, in August, 1850.
There have been three independent series of observations for the value of wave-time, made since October last, 1850.
The first experiment was repeated on several nights, between Seaton station and Portsmouth, Va. The distance on the iron wires is 269 miles, and the distance through the ground is 180 miles. The clock station excess, in the electrotonic readings, by a mean of 221 measures, was +08.024, while the computed excess for the assumed velocity of 15,400 miles per second, in the iron wires, was +08.035. The difference between theory and computation is, theory greater by +Q8.011.
The second experiment was made from Charleston, S.C., to Augusta, Ga., in the winter of 1851. The distance on the iron wire from Columbia (where the Charleston end went to the ground) to Augusta, was 301 miles, and from Augusta to Savannah 146 miles—making the total connexion through the iron wire 447 miles, and the distance through the ground, from Columbia to Savannah, 135 miles. The clock was at Savannah. The arbitrary signals were given at Charleston. The observed clock excess was by 59 measures +08.056. The computed wave-time, for the above assumed velocity, was +08.058, leaving a difference of +08.002.
The clock excess of Augusta above Savannah was, by observation, (forty measures,) +08.019; by theory, +0s.019; difference +08.000.
The third experiment was made at Cincinnati, on the 9th of May last, on the occasion of the meeting of the American Association for the Advancement of Science. The telegraph line was composed of 840 miles of iron wire, without ground connexion. The distances were as follows: From Cincinnati to Steubenville 295 miles; thence to Cincinnati the same; thence to Louisville 125 miles; thence to Cincinnati the same. The personal clock signals were given by Mr. Stager, chief operator at Cincinnati. In the first experiment the arbitrary signals were given by the operator at Steubenville, and recorded at Steubenville, and also on the two registers at Cincinnati, on opposite branches of the line. These registers I will call, respectively, Stager and Jones; Stager being the register for the clock station. The observed excesses were, for the Steubenville arbitrary signals, as follows: Stager-Steubenville.................... +08.040 by 31 measures. Stager-Jones .........
.......+0s.039 by 31. “ Again, for the Jones arbitrary signals, on the Stager clock scale, we found: Stager-Steubenville......
....-08.004 by 39 measures. Stager-Jones .....
..........+0s.050 by 226 "
The direction of the current from the platinum to the zinc, through the junction wires, was from Stager to Steubenville; thence to Jones; thence round by Louisville to Stager. This is the first experiment made by the Coast Survey on a telegraph line of iron wire exclusively, without ground connexion. The first conclusion to be drawn from this experiment is, that the excesses of the clock station readings, in the experiments heretofore made, have not been owing to the fact that a part of the galvanic circuit has been made through the ground, since they are here found to be as great for the dimensions of the line as in former experiments, with the partial ground connexions. This experiment was made with a long circuit of iron wire, without ground connexion. It confirms the general conclusion respecting the value of wave-time. It gives a new field for the discussion of the physical question whether the wave is propagated round in one direction, and only affects the magnets as it reaches them in succession in this direction, or whether the wave travels by the shortest direction from one magnet to another, without reference to the character of the poles. Our experiments with lines composed partly of ground and partly of iron wire stretched on poles, led to the preference of the latter view of the subject. The experiment at Cincinnati, in 1851, raises some doubt on this conclusion. It was made with a single battery at Cincinnati, and with 840 miles of wire, all in the air. The work of this night was not as complete as I could have desired. I must, therefore, wait till similar experiments are made, under more favorable circumstances, before attempting a further examination of the question.
38, 294 +2.496 2,051 From which it appears that the time of traversing 15,342 miles is one second. The column marked (obsd-comp'd) is based upon this value. Yours, respectfully,
SEARŞ C. WALKER, Assistant C. 8.
APPENDIX No. 26.
Abstract of reports on longitudes, by Sears C. Walker, assistant in the coast
survey, to the Superintendent.
CAMBRIDGE, September 30, 1851. DEAR SIR: I beg to submit an abstract of all my reports on longitude hitherto made.
Harvard Observatory, west of Greenwich.
h. m. S. (A) By moon-culminations at Harvard, 1843–1845....... 4 44 28.47 ' 66 66
Hudson, Ohio, 1838–1844.. 28.62 16 16 16 «
Wilkes' obs'y, 1838–1842... 28.52 6 16 16
Washington obs'y, 1845.... 28.06
(A) Mean by moon-culminations............
...4 44 28.42
(B) By eclipses, transits, and occultations
Weight. 66 At Dorchester and Harvard, 1820-1840......4 44 32.16 — 6.4 66 66 Brooklyn, New York.............
31.22 - 0.4 66 66 Philadelphia, 1769–1840...
32.56 — 2.5 " " Wilkes' observatory, 1838–1842....
33.13 – 1.0
" Mean by eclipses, transits, and occultations..4 44 32.27 -10.3
These phenomena have been reduced by Burkhardt's tables, and include, on the average, the constant error of his parallax of the moon. Airy, in his reductions of the Greenwich observations of the moon, makes the correction of this parallax to be A *.=+1".78. Professor Peirce and myself have computed the average value of the coefficient ()=-18.5, whence () .=-2s.67; and 4h. 44m. 325.27 -2s. 67 are
h. m. S. (B') Corrected mean by eclipses, transits, and occultations 4 44 29.60 (C) By chronometers with LiverpoolIndiscriminate mean of 373 chronometers in all.... 4 44 30.92 " 175 S Great special 2
Exp. of 1849 S Bond's o
(C) Adopting the last value..............
4 44 30.10
(A) Longitude of Harvard observatory
4 44 28.42 (B')
30.10 Adopted for the present, Harvard observatory ......... 4 44 29.05