nitude, seen by the naked eye; the coma seems diminished. more than half of its appearance, on the 6th of December, and the nucleus is equally surrounded by it on all sides, without any trace of tail, and so faint as very much to resemble some of the nebulæ. January 15th. Since the fifth instant the weather has been unfavourable for viewing the heavens; this evening is very serene and freezing; after a little search, I found the comet with the telescope, between two small stars in Lacertæ, the position of the comet was again unfavourable for finding its relative place by the micrometer of the reflecting telescope, but having armed my small achromatic telescope with one of Cavallo's pearl micrometers, I took the distance of the comet from two small stars, the angle at the comet being nearly a right one, as follows: At 7h 0 Comet N. easterly from 5 Lacerta 1° 14′ 12′′ of the 4th-5th magnitude, 7 5 Comet S. easterly from 4 Lacerte 1 24 48 of the 5th magnitude. The uncertainty may be between one and two minutes. In the great telescope, the comet is yet sufficiently conspicuous; the nucleus visible like a star of the eighth magnitude, in our purest atmosphere, and the coma but little changed since the 5th instant. January 17th. The last evening was cloudy and rainy, but the weather cleared up mild this evening, which enabled me to direct the same instrument with the pearl micrometer to the place of the comet, which was very obscure, though I succeeded in making the following observations: At 7h 0' Comet S. easterly from 7 Lacerta 2° 2′ 58" of the 4th magnitude, The uncertainty may be the same as on the 15th. February 25th. From the 17th of last month the weather continued long unfavourable, and I despaired of again seeing the comet; but thinking it of importance to get a view of it once more, in a more distant part of its orbit, I searched with great diligence and some anxiety, and at length found an object which I had no doubt was the comet, situated between Cassiopeæ and o Cassiopeæ; but as the objects were now descending upon the tops of the forest trees, I had not time to complete my estimate of its place that evening, but marked particularly its position with regard to certain stars both in the field of the large telescope, and in the finder; the comet was not visible in the last, but its position was known by the intersection of the cross-wires, which coincided exactly with the center of the field of the telescope, reserving to myself the ascertainment of its place by the aid of those stars, in case the comet could not be again discovered. For many days the weather was extremely unfavourable, and when it cleared up, I discovered the stars which had been noted, both in the field of the great telescope, and in the finder, but the comet had removed, and though diligently searched for along its supposed path, was seen no more. I now looked out for some known star, which might pass over the field of view of the telescope after the place of the comet, so as to be enabled to determine their difference in R. A. and declination; but none was to be found which would pass in any convenient space of time, and the place of the comet being now very low in the evening, I was obliged to make haste to approximate in the best manner now in my power; hoping in the course of some months to examine the subject again, when the part of the heavens where the comet disappeared should be conveniently seen in the eastern portion of the hemisphere. The place where the comet was last seen, is in the line joining the stars and o Cassiopeæ, and the difference of the comet's place in R. A. from o Cassiopea was found, from observation, to be 96 seconds in time; from whence we deduce the comet's place on the 25th of February at 8 to have been 8° 7' 6" in R. A. and 48° 30′ 58′′ north declination. This is given only as an approximation. No. LV. A Letter from Captain William Jones, of Philadelphia, to the President of the Society, communicating sundry queries proposed by him to William Jones Esquire, Civil Engineer of Calcutta, relative to the principles and practice of building in India, with his answers to the same. DEAR SIR, Read June 17th, 1808. Philadelphia, June 17th, 1808. WHEN in Calcutta, I had the pleasure to become acquainted with Mr. William Jones, whose profession is that of a civil engineer, and who at the time was employed in constructing a dry dock of great capacity, calculated to receive a man of war when the water of the Ganges was at the lowest. He is distinguished as a man of genius, of much philosophical knowledge, and of great practical experience in all the branches connected with his profession. He regretted that the urgency of his pursuits precluded him from rendering his remarks more perfect and comprehensive than the papers herewith enclosed; and proffered a correspondence with me on any subject which I might deem interesting. Should the Society desire information, from that quarter, on any subject of philosophy, natural history, or the mechanic arts, I will cheerfully avail myself of his kind offer. You will perceive that Mr. Jones has said nothing relative to public roads-he did not consider the manner of constructing them in that country as applicable to this. I know not whether there is any thing in the communication I have to make, that will be new or interesting to the Society; if not, I trust the desire to be useful will constitute my claim to indulgence. I am, very respectfully, yours, WILLIAM JONES. D d Copy of a letter from William Jones of Philadelphia, to William Jones Esquire, Civil Engineer, of Calcutta. MY DEAR SIR, Calcutta, December 26th, 1807. Your obliging assent to my solicitation for a memorandum of the manner of constructing a terrace roof in this country, and a desire to avail myself of such information relative to the arts of other countries, as may be useful in my own, prompts me to ask of you a brief communication of the principles and practice of building in India, with such observations as your experience may suggest. I look for indulgence, in the liberality of sentiment and love of science and the arts, which general suffrage has attached to your character. A desire of individual information alone, could not have induced me to trespass on time and attention so assiduously and usefully employed, but my intention is, to present your communication to the American Philosophical Society at Philadelphia, which will unite with its associate in a just sense of the obligation. A knowledge of the composition of cements, and of the quality and combination of materials employed in architecture in India, the excellence of which has been consummated by the lapse of ages, is an object of great interest in America. The structure of public roads is no less so: I am told there are some very excellent in India; any information on that subject, with a view to economy, durability, and a solidity impervious to intense frost, will be highly acceptable. I beg leave to present a few queries connected with the object in contemplation.-They are suggested by the local circumstance of climate and architecture in America. 1st. What are the materials, and what is the quality of the cement, used in constructing the walls of buildings in India? 2d. Are the walls below the surface, of the same materials? Sd. What is the thickness of the exterior, as well as of the interior walls, in proportion to the elevation? 4th. What are the component parts of the plaister of the exterior and interior walls? 5th. How, and of what materials, is the roof formed? 6th. What is the thickness of the terrace on the roof, the process of laying it, and the composition of the materials? 7th. What are the proportionate dimensions, and what is the relative strength to oak timber, of the beams which sustain the roof? 8th. Is the thickness of the walls deemed necessary to sustain the incumbent weight of the roof alone, or is it partly to resist heat-or is the extraordinary thickness in consequence of the fragile quality of the brick? 9th. Do you think a roof so constructed capable of resisting the intensity of the frost in North America? 10th. Is a horizontal roof, so constructed, capable of sustaining any great additional weight, such as the superincumbent weight of snow, which, in America, is frequently three or four feet deep? 11th. How, and of what materials are the floors constructed; and what is the quality and thickness of the cement which forms the floor? 12th. What is the proportionate elevation of the ceilings? 13th. What is the quality, and what are the component parts of the water cement, used in India, and of the celebrated cement and plaister used at Madrass? 14th. Is shell or stone lime preferred, and does the lime of India possess any intrinsic superiority over the shell or stone lime of Europe or America? 15th. Does sugar, molasses, or animal or vegetable oils, form a part of any of the cements used in India? 16th. I am told that the iron exclusively used in the fastening of all ships built in India, (even that which secures the sheathing boards) is completely protected from the corrosive effects of the copper, by the coat of Chunam [lime and animal or vegetable oil thoroughly amalgamated] one fourth of an inch thick, which is between the main plank and the sheathing boards, and also between the latter and the copper sheathing; and that the iron of coppered ships has been found in perfect preservation after ten years' service. Do these facts come within your knowledge? |