if the difference of height of this thermometer, at the two stations, be called d, we shall have d= 0.452 X D; for d: D:: 81.4: 180 :: 0.452 : 1; and the number of degrees expressed by d, will show immediately the correction for the difference of heat of the two barometers. If the thermometer, designed to show the temperature of the air, be divided with the interval between freezing and boiling water 200, and the freezing point be marked-9, and the boiling point+191, and the heights of this thermometer, at the two stations, be called G and 1, we shall have F 40 449 G+ I 2 × 500 = G+ I 1000 For F 40 F - 328, is the height of Fahrenheit's thermometer, reckoned from 8 degrees above freezing, and 449: 500 :: 180: 200; 8: 9, and the fraction F- 328 449 if both the numerator and denominator be increased in the ratio of 449 to 500, 32) X. Therefore, if the thermometer of the barometer has the freezing point marked 0, and the point of boiling water 81.4, and the difference of its height, at the two stations, be called d; and the thermometer for measuring the temperature of the air, 'be divided with the interval of 200 between the freezing point and that of boiling water, and the first be marked - 9, and the latter + 191, and the degrees shown by this, at the two stations, be called G and 1; the formula, that will give the height of the upper station above the lower one, in English fathoms, will be (log. Blog. b d) × (1+ + ;) which conse G+ I 1000 quently multiplied by 6, will give the height in English feet. It is to be observed, as before, that ➡d or + d is to be used, according as the thermometer, attached to the barometer, is highest at the lower or upper station; and if G and I should happen to fall below O of the scale, or to be subtractive, they must be applied accordingly in the calculation. I shall now add nothing more, but to give the rule for finding heights by the barometer, according to the formulæ delivered above, in common language; first, as adapted to Fahrenheit's thermometer, and next, as adapted to the 2 thermometers of particular scales. Take the difference of the tabular logarithms of the observed heights of the barometer, at the two stations, considering the first 4 figures, exclusive of the index, as whole numbers, and the 3 remaining figures to the right as decimals, and subtract or add of the difference of the altitude of the Fahrenheit's thermometer, attached to the barometer at the two stations, according as it was highest at the lower or upper station; thus you will have the height of the upper station above the lower, in English fathoms nearly to be corrected, as follows: make this proportion; as 449 is to the dif ference of the mean altitude of Fahrenheit's thermometer, exposed to the air at the two stations, from 40°, so is the height of the upper station found nearly, to the correction of the same: which added or subtracted, according as the mean altitude of Fahrenheit's thermometer was higher or lower than 40°, will give the true height of the upper station above the lower, in English fathoms; and multiplied by 6, will give it in English feet. The same rule, adapted to the thermometers of particular scales, is this: take the difference of the tabular logarithms of the observed heights of the barometer, at the two stations, considering the first 4 figures, exclusive of the index, as whole numbers, and the 3 remaining figures to the right as decimals; and subtract or add the difference of the thermometer, of a particular scale, attached to the barometer, at the two stations, according as it was highest at the lower or upper station, and you will have the height of the upper station above the lower one, in English fathoms, nearly; to be corrected as follows: make this proportion; as 1000 is to the sum of the altitudes of the thermometer of a particular scale, exposed to the air at both stations, so is the height of the upper station above the lower, found nearly, to the correction of the same; which added or subtracted, according as the sum of the altitudes of the thermometers, exposed to the air, is positive or negative, will give the true height of the upper station above the lower in English fathoms; and multiplied by 6, will give it in English feet. XXI. Eclipses of Jupiter's Satellites, observed near Quebec. By Sam. Holland, Esq., Surveyor General of Lands for the Northern District of America. p. 171. These eclipses of Jupiter's satellites were observed at a house, bearing south 36° west from Quebec, distant from the castle of St. Lewis 24 miles, with Dollond's long reflecting telescope. XXII. Observations of the Immersions and Emersions of the Satellites of Jupiter, taken in 1768, by Ensign George Sproule, of H. M. 59th Reg., on the South Point of the Entrance of Gaspee Basin, which bears from Cape Ferrilong, or the Cape forming the Bay to the Northward, N. 68 W. by the true Meridian, distant 12 Marine Miles. Communicated by the Astron. Royal. p. 177. The latitude of the place of observation, at Gaspee, accurately determined, was 48° 47′ 32". The variation of the needle, by repeated trials different ways, was 16° 30′ w. XXIII. Astronomical Observations made by Samuel Holland, Esq., Surveyor The latitude by repeated observations, 43° 4' 27" N. Observed, with Dollond's 12-feet refracting telescope, immersion and emersions of 's satellites as follow. 1771. April 11th, an immersion of the 1st, at.... 27th, same May 4th, same... ..... The variation of the compass at this place, is 7° 46′ west. Apparent time. 15h 43m 30s 14 1 43 15 55 54. Portsmouth, province of New Hampshire, the latitude by repeated observations, 43° 4' 15" N. Observed, with Dollond's 12-feet refracting telescope, immersions and emersions of 's satellites as follow. The variation of the compass at this place is 7° 48' west. 7 50 0 6 57 44 XXIV. Observations of Eclipses of Jupiter's first Satellites made at the Royal Observatory at Greenwich, compared with Observations of the same, made by Samuel Holland, Esq., and others of his Party, in several Parts of North America, and the Longitudes of the Places thence deduced. By the Astronomer Royal. p. 184. The result of those comparisons, give the following longitudes of the places of observations. XXV. Immersions and Emersions of Jupiter's first Satellite, observed at Jupiter's Inlet, on the Island of Anticosti, North America, by Mr. Thomas Wright, Deputy Surveyor General of Lands for the Northern District of America; and the Longitude of the Place, deduced from Comparison with Observations made at the Royal Observatory at Greenwich, by the Astronomer Royal. p. 190. These observations were made at Jupiter's inlet, 2 leagues to the westward of the south-west point of the island of Anticosti, situated at the entrance of the river St. Laurence, in latitude 49° 26' north, with a 2-feet reflecting telescope of the late Mr. Short's construction. Mr. Wright's observations of the eclipses of Jupiter's first satellite, corrected, are as follow: The mean difference of meridians by the 4 immersions is 4h 15m 1918, and by the 5 emersions is 4h 14m 451; both which ought to be corrected, by the help of the nearest observations made at the Royal Observatory at Greenwich. The immersions and emersions observed there, proper to compare with the preceding observations, are these: all observed with a 6-feet reflector, which, I reckon, shows an immersion of the first satellite 20s later, and an emersion of the same as much sooner, than a 2-feet reflecting telescope. The correction of the Nautical Almanac for a 6-feet reflector, by the mean of the 2 immersions, is 43s, which applied to 4h 15m 1915, the longitude of Jupiter's inlet found from immersions, by the help of the Nautical Almanac, gives 4h 14m 36, the difference of longitude deduced from the immersions. The correction of the Nautical Almanac, by the mean of the 6 emersions, is — 16", which applied to 4h 14m 451", the longitude of Jupiter's inlet found by the emersions, by the help of the Nautical Almanac, gives 4h 14m 29, the longitude deduced from the emersions. The mean of these 2 results, found from the immersions and emersions separately, is 4h 14m 33s the proper difference of longitude of Jupiter's inlet west of Greenwich. I have here made no allowance for the difference of power of the 2-feet reflector, used at Jupiter's inlet, and the 6-feet reflector, used at Greenwich; because the mean is taken between the results from the immersions and emersions; which method includes that correction; that is to say, gives the same result whether that correction be made or not. From the foregoing comparisons it should seem that the air is much clearer at the island of Anticosti than at Greenwich, which Mr. Wright confirmed to me, since the immersions give the longitude only 7s greater than the emersions; which shows that Mr. Wright observed an immersion only 4$ sooner, and an emersion as much later, with a 2-feet reflector, than was done at Greenwich in a 6-feet reflector; though, in an equally good air, this latter telescope would have had the advantage of the former by 20°, instead of 4. XXVI. Extract of a Letter from Mr. Humphry Marshall, of West Bradford, in Chester County, Pennsylvania, to Dr. Franklin, sent with Sketches of the Solar Spots, dated May 3, 1773. p. 194. The appearances of these spots were not engraven. Mr. M. says he is of opinion that the spots are near the sun's surface, if not closely adhering to it, for these reasons: 1. That their velocities are apparently greatest near the centre, and gradually slower towards each limb. 2. That the shape of the spots varies, according to their position on the several parts of the sun's disc; those that appear broad, and nearly round, when on the middle, seeming, at their first. appearance on the eastern limb, but as lines; and, as they advance towards the centre, become oval, then round, and, in their progress to the western limb, appear again, as ovals and lines. His other remarks were, that the spots were 124 days, and about 2 or 3 hours, in passing; that though some continued visible from one limb to the other, a few would disappear, after having been visible several days; and others divided into parts; that scarcely any spots ever appeared beyond what may be called the polar circles of the sun; and that the same spot never appeared a 2d time, on the eastern limb, at least not in the same form and position. XXVII. Account of the House-martin, or Martlet. By the Rev. Gilbert White. p. 196. Reprinted in Mr. White's History of Selborne. |