# Observations of the Transit of Mercury, May 4, 1786, at Dresden. By M. Kohler, Inspector of the Mathematical Repository of the Elector of Saxony; Communicated by the Count De Bruhl, F. R. S. **Author(s):** M. Kohler, Count De Bruhl **Year:** 1787 **Journal:** Philosophical Transactions of the Royal Society of London **Volume:** 77 **Pages:** 2 pages **Identifier:** jstor-106710 **JSTOR URL:** --- IX. Observations of the Transit of Mercury, May 4, 1786, at Dresden. By M. Köhler, Inspector of the Mathematical Repository of the Elector of Saxony; communicated by the Count de Brühl, F. R. S. Read December 21, 1786. Apparent time. 9 21' 54" beginning of the planet's egress, doubtful. 9 25' 23" complete egress, or last contact, very certain. The telescope with which Mr. Köhler observed, was a 9-feet refractor of Dollond's, magnifying 104 times. He has made a comparison of his observation with that of Alexander Aubert, Esq. from which he has inferred the longitude of Dresden in the following manner. | Exterior contact observed by Mr. Aubert at | Mean time. | |------------------------------------------|------------| | Equation | + 3 28,3 | | Difference of parallax | + 0 13,4 | | Apparent time at Loam-pit Hill | 8 30 46,7 | | Loam-pit Hill west of Greenwich | + 0 5,4 | | Apparent time at Greenwich | 8 30 52,1 | | Apparent time at Dresden | 9 25 23,0 | Longitude of Dresden east of Greenwich 54 30,9