St. Andrew's or the Old Church, at Plymouth. The angle at Butterton, between the Old Church tower and Kit Hill, is 37° 45′ 5′′,2; its bearing, therefore, south-west from the meridian, is 75° 1′ 56′′; consequently, its distance from the meridian is 57505 feet, and from the perpendicular 15374 feet. These respectively subtend 9′ 24′′, and 2' 32′′,1: hence, its latitude becomes 50° 22′ 13′′,6, and longitude 4° 7′31′′,6= 16m go',1 in time, west of Greenwich. As it is of very great importance that the truths of the conclusions given in this Work should receive support, wherever I can find it, I think it right to mention the result of his Excellency the Count de BRUHL's endeavours to ascertain the longitude of Plymouth, by means of chronometers. The following is a copy of his communication, made in the year 1795. Journey from Plymouth to London. Green Timekeeper. June 8th, Mr. MUDGE'S clock* at Plymouth, fast for mean time oTM 32',15 Timekeeper faster than Mr. MUDGE'S clock 1783. Timekeeper slower than London clock O 25,6 14 29,4 O 36,5 Mr. MUDGE's clock at Plymouth, fast for mean time om 32',15 June 8th, Timekeeper faster than Mr. MUDGE'S clock [Timekeeper slower than London clock O 37,4 14 17,2 14th. London clock slow for mean time Difference of longitude o 36,5 16 3,25 Mean difference 16 3,55 The longitude of St. Paul's, west of Greenwich, is 23,1 in It is, perhaps, right to observe, that Mr. T. MUDGE's transit, at Plymouth, was made by the late Mr. BIRD, and properly set up between stone pillars. The clock, the entire work of his own hands, was a most excellent one. time; and Mr. DUTTON's house in Fleet-street is about 2 west of St. Paul's; wherefore, its longitude west of Greenwich is 25': consequently, 16m 3',55 + 25o = 16m 283,55, is the difference of longitude between Greenwich and Plymouth, as shewn by the timekeepers. Now the meridian of Mr. MUDGE's transit-room, at Plymouth, passed only 35 feet to the eastward of the centre of St. Andrew's Tower, his northern meridian mark being on the church itself; therefore, the longitude of the church and transit-room may be considered the same. From the survey, we find it to be 16m 30,1; and, from Count BRUHL's determination, making a just allowance for the difference of longitude between the late Mr. DUTTON'S house and Greenwich, 16m 283,5. It is left for the public, and this learned Society in particular, to determine how far the near agreement of these several methods, tends to corroborate the assertion I have advanced, of the dependence which may be placed on the deductions drawn from the observations made at Beachy Head and Dunnose. If there had been only one watch employed on the occasion, the result would not have been so satisfactory as the circumstance of two being used seems to make it. As the occasion calls for the remark, before I dismiss this article, I must observe, that the highest advantages would accrue to geography, were the ideas of the Astronomer Royal carried into execution, (and which I shall endeavour to do at some future period,) respecting the discovery of the difference of longitude between Greenwich and some very remote point on the western side of the island, (St. David's Head for instance,) by means of timekeepers, According to HORWOOD's Map of London, the distance from the centre of St. Paul's to Bolt Court, at the corner of which Mr. DUTTON's house is situated, is 31 chains. carried backwards and forwards in the mail coaches. If this excellent scheme were executed, and the watches employed equal to the best now made, it is probable that the true difference of longitude would shortly be determined. The geodetical situation of St. David's Head will, ere long, be ascertained from a prosecution of the survey: a knowledge, therefore, of its true longitude would be attended with eminent advantages. Lizard Light-Houses. The light-houses on this head-land were observed from Pertinney and Karnbonellis. At the latter, Pertinney bears 74° 22′ 41′′ south-west, from the parallel to the meridian of St. Agnes; and, as the angle between the western light-house and Pertinney is 78° 40' 5", it follows, that the bearing of the lighthouse from the said parallel is 4° 17′ 24′′ south-east. Computing with this angle and the distance from Karnbonellis to the lighthouse, we get 3344 feet, and 126499 feet, for the distances of that object from the meridian and perpendicular of St. Agnes: therefore, admitting the length of the degree in the meridian, in the middle point between St. Agnes and the light-house, to be 60850 fathoms, and 61182 for the length of a degree of a great circle perpendicular to it, we get 20' 47",4, and 32′′,8, for the small arcs which those spaces respectively subtend. These data, with the latitude and longitude of St. Agnes, 50° 18′ 27", and 5° 11′ 55",7, give the latitude of the light-house 49° 57' 44", and longitude west of Greenwich 5° 11′ 4′′,8, in time, 20m 443. This light-house was also observed from the station on Karnminnis. The triangle resulting from that observation, together with the angle at Karnbonellis, is Western Light-house 37 48 44; which gives 81342 feet, for the distance between the station Karnbonellis and the Light-house. This distance is said, in the Philosophical Transactions for 1797, p. 501, to be 81348 feet, which differs only 6 feet from the above determination; but it is probable the distance first given is most correct, as the two light-houses appearing nearly in the same line at Karnminnis, was the means of preventing us from clearly distinguishing the apex of either, and it was principally on this account that we preferred the observation made at Pertinney. The agreement however proves, that no inconsistency can be found to obtain with respect to the data before given, for settling the situation of this important headland. In the Philosophical Transactions for 1797, page 502, it is mentioned, that the distance from the spot where the late Mr. BRADLEY made his observations, to the place where his meridian mark was fixed, was 800 feet. But there appears to be some inconsistency in this particular; as Mr. BRADLEY'S own words, in an extract of a letter now before me, are, it was just 480 feet. Adding to this, 24 feet, the distance between the place of the meridian mark and the line joining the centre of the lighthouses, we get the distance of the point O, or the place of the Observatory, (see Phil. Trans. 1797, p. 502,) from the line joining the light-houses W, E, 504 feet; a space corresponding to 5" of latitude, nearly; therefore, from the trigonometrical operations, we get, Mr. BRADLEY'S observations for finding the latitude, were made with a quadrant of one foot radius, the workmanship of Mr. BIRD; they were as follows. Nine meridional altitudes of the sun's limb, the extreme results of which were 49° 57′ 27',5 and 49° 57′ 44", gave for the latitude of the Obser- Six meridional observations of the Pole Star be- α realis, and Serpentis, the extreme results of which were 49° 57′ 54′′,7 and 49° 57' 2",7, gave for the latitude Fifteen observations of a, B, y Draconis, the extreme results of which were 49° 57′ 22′′,2 and 49° 57′ 2′′7, gave for the latitude The mean of which is 49° 57′ 35′′ 49 57 23,2 49 57 29 49 57 33 According to the trigonometrical operations, the latitude is 49° 57′ 44′′; there is, therefore, a difference of 14" between the results; a quantity so large as justly to excite surprise, if it were not generally understood, that much dependance cannot be placed on observations made with an astronomical quadrant precisely similar to that made use of by Mr. BRADLEY. The extreme results in the above, differ so widely as to authorise the truth of the supposition on this occasion. The longitude of the Lizard was determined by the transit of Venus, Sun's eclipse, transit of the Moon, and two emersions |