Table I. column 1. is deduced by taking the difference between NPD 1755* and the NPD 1800+, and reducing the rate for 10 years, for change of precession, to 1818. Column 2. in like manner, from Palermo Cat. 1800, and Dublin Cat. 1823 §. Mr Pond's observations 1800 were made at Westbury .. There are two ways of considering the results in the above Tables. (1.) Mr Pond deduces, that the variations in NPD are irregular; and he supports his conclusion by the observations from which the numbers in Table 2. are computed. If his observations are exact, this remarkable consequence follows, that the errors of observation at Palermo and Dublin have made the variations in Table 1. appear constant, which are really changeable. (2.) If we consider Table 1. as supporting an uniform variation in NPD of each star, and there is no greater differences than what might be expected from the unavoidable errors of observations, then it follows, that the Palermo and Dublin observations are more exact than the Westbury and Greenwich ob servations. 2. Comet of September 1822, observed at Paramatta.—The following are the elliptic elements of the comet observed at Paramatta by Sir Thomas Brisbane and Mr Rumker, as communicated to the Royal Society of Edinburgh. Time of passing the perihelion, mean time, Oct. 24,221201 3. Anomaly in the Figure of the Earth. So many ships touch at Madeira, and take a new departure from it, that the longitude of the island is a matter of considerable importance. Dr Tiarks was therefore sent out by the Board of Longitude to Bessel, Astron. Fundament. + Piazzi, Great Catalogue of 1814. § Phil. Trans. 1806. For Mr Pond's Observations, see Phil. Trans. 1815, and 1823, Part I. ascertain it, with sixteen watches, in the summer of 1822; and a remarkable circumstance occurred, which was not within the object of his original mission. For, in going from Greenwich to Falmouth, a difference of longitude was found equal to 20′ 11′′.49; and, in returning from Falmouth to Greenwich, a difference of 20′ 11′′.13. Now, the difference, as determined from the Trigonometrical Survey (given in the third edition of the requisite tables), is only 20' 6".9; and this variation made it expedient to engage Dr Tiarks to verify his observations in the Channel. He was furnished with twenty-nine chronometers, and was employed from the latter end of last July till the middle of September in sailing between Dover and Falmouth. His results are as follows: From hence it is clear that the figure of the earth must be somewhat different from that assumed for determining the longitudes from the Trigonometrical Survey, and that about 5′′ must be added, in the latitude of the Channel, for every 20′ of longitude which is deduced from it. 4. Reported Inaccuracy of M. Bessel's Catalogue.—A report relative to an inaccuracy in M. Bessel's Catalogue having not only gone abroad, but having found a place in the Annals of Philosophy for November, p. 397, we are happy to have it in our power to contradict this rumour by the following extract of a letter, from M. Bessel, to a gentleman in London: -"With respect to my Catalogue of the declination of the principal stars, I think the information you sent me must be founded on some misunderstanding, as I have not the least suspicion that it is wrong. The effect produced by the bending of the telescope of my circle appears to me to be so well determined, that on this point I can expect no further improvement, without running the risk of greater inaccuracies. In my method both of observation and computation, I have never neglected any thing that could have any influence of consequence. I cannot, therefore, throw any light on what you mention, unless some one would point out inaccuracies at present unperceived by me, which would produce an alteration. The whole of my proceedings are laid open to every astronomer, in the seventh number of my Observations; and those who devote to them an attentive examination, will have greater confidence in what I have stated, than by listening to any idle reports." 5. Anomaly in the Observations at Arbury Hill.—In levelling from the station of Arbury Hill to the Grand Junction Canal, Mr B. Bevan found that the country to the north of Arbury station fell suddenly about 400 feet, and continued at this depressed state for nine or ten miles. He therefore conceived that this defect of matter to the north of the station was a reason for supposing a deflexion of the plumb line to the southward, In order to ascertain the truth of this supposition, he computed the latitude of Arbury station from that of Blenheim, determined independent of any astronomical observation made at Arbury, and he found it five seconds LESS than that shewn by the zenith sector; thus countenancing, in a high degree, the probability of local attraction by the high land to the south of the station. See this Journal, vol. i. p. 200. The following are the heights of the station which he found by levelling. See Phil. Trans. 1823, p. 73—77. 6. Sir Thomas Brisbane's Experiments on the Pendulum.By means of a pendulum belonging to the Board of Longitude, and similar to that used by Captain Kater and Captain Hall, Sir Thomas Brisbane made a series of experiments at Paramatta, in 1822. The pendulum having been swung in London, and observed both by Captain Kater and Sir Thomas Brisbane, it was found that it performed 86090.17 vibrations at London, in Lat. 51° 31′ 8′′.4, in a mean solar day, at 60° of Fahrenheit, and in a vacuum. At Paramatta, in E. Long. 151° 0′ 15′′, and S. Lat. 33° 48′ 43′′, the same pendulum performed 86021.59 1 295.84 vibrations, according to Sir Thomas Brisbane's observations, and 86022.21 according to the observations of Mr Dunlop, his scientific assistant. By comparing Sir Thomas's results with those made in London, Captain Kater has found that 39.07696 inches is the length of the pendulum vibrating seconds at Paramatta; .0052704 the diminution of gravity from the Pole to the Equator, and the resulting compression, the secondspendulum at London being taken at 39.13929 inches. By comparing the same experiments with those made by Captain Kater, at Unst, in Lat. 60° 45′ 28′′ N., the diminution of gravity is .0053605, and the resulting compression. comparing the results of Mr Dunlop's observations with his own in London, Captain Kater finds the length of the seconds-pendulum at Paramatta to be 39.07751, the diminution of gravity 1 303.95 By Comparing these with the Unst observations, the diminution of gravity is .0053292, 7. Experiments on the Velocity of Sound-A very valuable and elaborate series of experiments on the velocity of sound has been made at Madras, by Mr Goldingham. Various different measures of the velocity of sound had been obtained by different observers, but the discrepancies in their observations were not supposed to arise from the condition of the atmosphere. Mr Goldingham made his experiments with two guns, at the distances of 29,547 feet and 13,932.3 feet. They were 24-pounders charged with 8 pounds of powder, and the experiments were continued during the latter part of 1820, and the whole of 1821. The following table contains the substance of these numerous and well-conducted experiments; and it is curious to remark, how the velocity gradually increases towards the middle of the year, and again gradually diminishes. Mr Goldingham conceives that this regularity would be still greater, with the mean of several years observations. Mr Goldingham concludes, that for each degree of the thermometer 1.2 feet may be allowed in the velocity of sound for a second; for each degree of the hygrometer 1.4 feet; and for ath of an inch of the barometer 9.2 feet. He concludes that 10 feet per second is the difference of the velocity of sound between a calm and in a moderate breeze, and 214 feet in a second, or 1275 in a minute, is the difference, when the wind is in the direction of the motion of sound, or opposed to it.—See Phil. Trans. 1823, p. 96-140, and pp. 177, 178. of this Number. MAGNETISM. 8. Magnetism of Titanium, Cobalt and Nickel-Dr Wollaston having formerly been of opinion, (see this Journal, vol. ix. p. 403.), that the entire crystals of Titanium were not attractible by the Magnet when they were freed from adhering particles of iron, had occasion to re-examine them, and found this opinion incorrect. Although the crystals are, in this state, not sufficiently attractible to be wholly supported by the magnet; yet, when a crystal is supported by a fine thread, the force of attraction is sufficient to draw it about 20° from the perpendicular, and, consequently, the force of attraction is equal to about one-third the weight of the metal. A cubic piece of soft iron, of the same size, and weighing half a grain, had its attrac tive force to the same magnet such that it was able to lift from 80 to 90 times its weight of a silver chain. Cobalt carried from 50 to 60 times its weight; and Nickel from 20 to 30 times its own weight. Dr Wollaston considers that the presence of th 1 -250 |