number of later date, have each adopted different theories and conclusions, as to those attractive bodies, but generally concede that the cause is within the bowels of the earth, and near the poles. The first discovery of the variation of the magnetic needle was in the year 1492, by Columbus, in his first voyage to America, but it was not until the year 1580, that the subject was carefully studied and thoroughly investigated at London, when the variation was found to be 11° 50′ E., and in 1620 but 6° E., and in 1634, 4° 5' E., but in the year 1660 the pole pointed due north. In 1672, it was found to be 2° 30′ W., and in 1692, it was 6° W. In Paris the needle pointed due north about nine years after that at London. At present through Europe, Africa, and a part of Asia, the declination is to the west, but advancing eastward at the rate of one degree in 19 years. It is, however, ascertained that the declination never exceeds 15° on or near the Equator, but increasing towards the poles to 60°. Another surprising quality discoverable in the needle, is its inclination or dipping, that is, the magnetic power produces a double effect on needles. This, as well as the declination, deserves to be every where carefully observed and noted; in London I believe the inclination to be about 68°. In July 1820, Mr. Sabine observed the inclination of the needle at Melville Island, in lat. N. 75°, W. lon. 110°, found it to be 88° 43' 5". The following observations and calculations were made chiefly in the State of Vermont; partly by Dr. Samuel Williams, the more recent by the writer: In the year 1785, the declination of the needle at Montreal was 8° 24′ W., and at Quebec, 12° 50′; in 1794, 12° 20'. On the north line of Vermont in the year 1785, the variation was 7° 40′ W., and at Missisque bay the same year, 10° 10' W., and in 1828, but 8° 50'. In Pownall in 1786, the variation was 5° 50′ W., and in 1828, but 4° 10'. At Rutland in the year 1789, the variation was 7° 5′ W., and in 1818, 6° 10′, and in 1828, 5° 40′, and in 1848, 4° 39'. At Burlington in the year 1793, the variation was 7° 30', and in 1828, but 6° 45′ W. At Brandon in the year 1820, the variation was 5° 20', and in 1830, 4° 50' W. At Pittsfield, Vermont, in the year 1825, the needle varied 6° 5' W., in 1826, 6° 2', in 1830, 5° 50', and in 1836, 5° 34' West. In New Haven in 1820, the variation was 4° 25' 25", according to Professor Fisher, who supposes the annual variation to be 2' 45" eastward, but from personal observations made by the writer, the variation is found to be something over three seconds. From the above view it is no way surprising that so much litigation has arisen in consequence of surveys being made at different periods of time with little or no attention to the annual variation, and unless there is some method adopted to make it the duty of every practicing surveyor to ascertain from time to time the true variation, and note it as before observed, different cources will be run, and litigation continue. Mr. Dewit truly remarks, "that in years past, a rule has been prescribed for obtaining an approximate meridian supposed sufficient for common purposes, that is, to take the direction of the Pole star when in the same vertical line with Alioth, which is the first star in the tail of the Great Bear." This rule was once correct, but it is more than a century since, that the interval between the time when these two stars are in the same vertical, and the time when the Pole star is in the meridian, has been gradually increasing, on account of the annual increase of the right ascension of the Pole star than of Alioth. According to Blunt's table for the year 1805, we find that in lat. 42° 30' the elongation of the Pole star was 2° 20′ 51′′; and in the year 1837, I found it to be but 2° 7' 2" in the same lat.; and in 1839, 2° 6' 7", and in 1840, 2° 5' 41". In lat. 42° in the year 1837, 2° 5' 52", in 1848, 2° 5' 26", and in 1839, 2° 5′ 0′′, and in the year 1840, 2° 4′ 34′′. These annual variations will show the importance of a strict attention to time and place of observation. Various methods have been instituted to ascertain an accurate variation, but with much inaccuracy, and I apprehend that the main difficulty is in the finding a true meridian. The following is therefore recommended, being simple and the least subject to error: viz., by measuring the angle formed between the magnetic meridian and a line formed by the Pole star when on the meridian. But in this process it is necessary to know that this star is due north but twice in twenty-four hours. The time may be found by observing when the star Alioth, and the star Gamma, and the Pole star, are vertical; but when in a horizontal position, is at its greatest elongation on the side of Gamma. In order, therefore, to find a true meridian from the star, its declination must be calculated for the degree of latitude where the observation is made. This may be found by the following proposition:As the cosine of latitude is to radius, so is the sine of declination to the sine of elongation. The calculation may be also made as in the 6th and 7th cases laid down in Euclid's Spherical Trigonometry. According to the above proposition, the North star, in lat. 43° 30', January 1829, was in its declination 87° 47' 37", and its elongation 2° 13′ 22′′, and increasing at the rate of 19' 59" annually in the same latitude. In lat. 43° the same year the elongation was 2° 10′ 13". From the above dates and the application of the rules given, the variation of the magnetic needle is easily found in any latitude by a properly informed surveyor. CASTLETON, Vermont. ROCKS AND SHOALS IN THE PACIFIC. E. CHILD. The following list of islands, rocks, and shoals in the Pacific are not laid down on the charts : [In lat. 20° 30' N., lon. 152° 30' E., lies a small sandy bank, with heavy breakers, N. ៨៨៨៨៨៨៨ | z E. by N. of Nooaheva.] A group of islands.... [Lies a shoal, with from 5 to 15 fathoms.] [Two cables' length, discovered at 4, A. M., blowing a S. E. gale, ship going 9 knots. Narrowly escaped shipwreck.—Sydney Herald.] [18 miles S. E. of the island Amagura lies a small low island, and about West from it, at 4 miles distance, lies a dangerous reef, two cables' length, E. by N. from Robert's island.] [Sydness, 35 miles to the Eastward of its position on the chart.] Kound Killy harbor ... [The harbor of Ascension being very indefinitely laid down, and a great many exceptions, extends to the North-east of the island, 40 miles long.] Reef 80 miles long....... 7 21 N. 156 30 E. [This reef the ship Isabella was lost upon, bound to Manilla, observed on the reef.] 23 32 S. 162 52 E. 3 30 S. 176 2 E. 6 52 N. 158 24 E. Grimes' island, ship Jean..... 9° 16' N. 145° 43' E. [Six miles in circumference.] Mumford's shoal, 18 miles S. by W. W. from Vetthone island. ENGLISH AND AMERICAN IRON COMPARED. We have received a letter from a highly responsible house in Philadelphia, extensively engaged in the manufacture of iron in Pennsylvania, calling our attention to an extract we made of an article from the "Ledger" of that city. Our correspondent says:" It gives so unjust and unfair a representation of the case and of the facts, as stated by the Ledger's correspondent, that we herewith mail you the Ledger, containing the article in question. By a reperusal of this, you will perceive that the difference in value between English and American iron, according to the experience of the Reading Railroad Company, is thirteen dollars and fifty cents per ton, and not, as would appear by your extract, fifty-four cents. This arises from your stopping in the midst of the statement-fifty-four cents is the difference in the labor cost of repairs, in laying down so much more of the inferior iron. The statement was prepared by the Engineer of the Reading Railroad for Mr. Tucker, the President. We do not know how it fell into the hands of the Ledger, but recognize the statement as the same as the one we had previously received from Mr. Tucker." In order to correct an error of "omissior" rather than one of "commission," and set the matter right, we cheerfully comply with the request of our correspondent by transferring to the pages of the Merchants' Magazine the whole article as follows :— READING, October 26th, 1851. I promised, in my last letter, to furnish you with a comparative statement of the wear and tear of English and American rails, for the purpose of showing that the iron used in English rails has for the last five or six years materially deteriorated, a very inferior quality of the metal having been substituted for that formerly employed, with a view, probably, of "circumventing" the Tariff of 1846. On the other hand, our own improvements in the manufacture of railroad iron have kept pace with those in other branches of industry, so that, though the first cost of American rails is greater than that of imported English rails, yet, in the long run, the use of American rails proves to be cheaper and more economical. Unfortunately for new companies, the cheap article, at first cost, competes but too successfully with the superior high-priced one, and an immense amount of tribute is, in consequence, annually paid to the British ironmasters, that had much better, and much more profitably, be invested at home. The Reading Railroad, doing a larger business than any other railroad in the country, and carrying at all times and hours heavy freights, is probably better qualified to test the use of different kinds of rails, and I have accordingly procured from the officers on the road the following statistics of their respective wear and tear. The average yearly per centage of rails worn out on the road for the two years ending on the 1st of December, 1849, has been as follows: This statement, however, does not exactly indicate the relative value of the several kinds of iron mentioned. The 45 and 52 lbs. rail, are both on the light track; yet it is the ten and eleven years' wear of the former which compares with the seven and eight years of the latter, and the five and six years of the 60 lbs. rail, which are compared, with the average of the first three years' wear of the Phoenixville American 60 lbs. rails; both of which latter patterns are on the loaded (coal) car track. The 45 lbs. rail is composed of a double refined English E. V. iron,* and, from several indications, has lost much of its original strength by eleven years' use under a heavy trade; yet it compares favorably with the 52 lbs. rail lately manufactured and brought to this country; notwithstanding the superior weight and freshness of the latter, which experience can only be accounted for by the inferior quality of the metal used in its manufacture. The 52 lbs. English rail is also a very good English iron, corresponding, in quality, nearly with the American iron from Phoenixville and Danville; whilst the English 60 lbs. rail (last employed on the road,) is of an inferior quality, similar to the present low-priced importations, as it is only the low-priced English iron that can be thrown on the American market at prices calculated to impair the vigor of American competition. About 33 per cent, or one-third of the wear of the Phoenixville 60 lbs. rail is due to its having to sustain the loaded instead of the light trains; and by continuing the assumption that the best American iron is equal to that used in the English 52 lbs. rail, the following may be considered as the comparative wear of rails on the Reading railroad. English, 4 1-10 per cent per annum. American, 1 4-10 per cent per annum. Difference in favor of the American, 2 7-10 per cent; or, otherwise stated, the cost of repairing these rails per annum, (considering the damaged iron taken out as worth half as much as the new iron put on the track,) will be as follows: Repairing English iron, per ton, per yard.. Do. American, 66 66 66 Difference in favor of American rails... 54 cts. In addition to this, we must make a proper allowance for the labor of replacing the bars, and for the greater wear of machinery running over constantly failing rails, items which will increase the advantage of the good iron at least 50 per cent on the 82 cents per ton per annum, and correspondingly enhance the advantage resulting from the employment of American rails. Thus it would seem that the dividend-paying capacity of a railroad is the same with English iron at $40 a ton, as with American iron at $534 per ton; or, in other words, it gives American iron an advantage of $13 per ton in quality; and any process of legislation that would favor the employment of American rails instead of the English, though it might add to the first cost of the road, would not increase but diminish its permanent expenditures. OBSERVER. RAILROAD CARS WITHOUT DUST. The only misery of railroad traveling in a dry time is the dust and cinders, but a Yankee is about to do away with that annoyance. He has hit upon a mode of ventilation and has constructed a passenger car that is entirely free from dust and cinders, be the day dry, hot, windy, or dusty as may be. The car has been tested on the Vermont Central Railroad, and the success of the experiment was most triumphant. A long drouth had prevailed, and the road was as dusty as it well could be. The day was hot, and a correspondent of the Boston Atlas who rode in the car from Northfield to the Junction, says: "Not only was the car kept perfectly free from dust and cinders, but there was a constant current of air circulating through it all the while, ventilating and cooling it in the most thorough manner. While all the other cars were uncomfortably hot and dusty, ours continued the whole way most comfortably the reverse, in both respects. This great invention, which should be adopted on every railroad in the country, and for the discovery of which its inventor will deserve the thanks of every railroad traveler, is as simple as its success has been apparent. The air is forced into the car from the top, through boxes so adjusted that the motion of the car drives in a strong current. This is protected from dust and cinders by a network of fine wire. The windows of the car are made to admit light, but not air, and are not to be opened. All the air admitted must be from above, and through the network, and it passes out again through A celebrated brand. |