TOL. LXXX.] 



PHILOSOPHICAL TRANSACTIONS. 



627 



ments commonly give the true place of Mars within the 4th part of a minute. 

 The error in longitude -f- 17^' signifies that the longitude in the tables is IT" too 

 small ; and that those l^j" are to be added to the calculated longitude, in order to 

 make it agree with the observed longitude. 



The inclination of Mars is taken in Cassini's tables 1° 50' 54''', and in the 

 tables of De la Lande and Halley 1° 5l' 0^. 



Mr. B. concludes this paper with the opposition of Mars according to the fore- 

 going observations. The opposition of Mars to the sun happened 1788, Jan. 7, 

 at 8^ 19"* 32^ true time ; the apparent geocentric longitude of Mars at that mo- 

 ment = 3' 17° 17' 8'', and the geocentric latitude = 4° 4' 3'^ n. Saturn was in 

 opposition to the sun, Aug. 29, 20^ 5l"» IV true time ; the apparent longitude 

 h) = IP 7° 31' 34'^, and latitude 1° 59' 33'' s. The new planet was in opposi- 

 tion to the sun Jan. 18, 0^ 28"™ 33' true time, the longitude = 3' 28° 10' 7", 

 and latitude 0° 34' 35'' n. 



III. An Account of some luminous Arches. By Mr. Wm. Hey, of Leeds, F.R.S. 



p. 32. 



While Mr. H. was at Buxton, in March 1774, about half past 8 he saw a 

 luminous arch, which appeared very beautiful in the atmosphere. Its colour was 

 white, inclining to yellow ; its breadth in the crown apparently equal to that of 

 the rainbow. As it approached the horizon, each leg of the arch became gradually 

 broader. It was stationary while he viewed it, and free from any sensible corusca- 

 tions. Its direction seemed to be from about the n.e. to the s.w. at least its 

 eastern leg was inclined to the north, and its western to the south. Its crown 

 or most elevated part, was not far from the zenith. The evening was clear, and 

 the stars appeared bright. It continued about half an hour after it was first ob- 

 served by the company. 



In October 1775, he saw a similar arch at Leeds, of the same colour, breadth, 

 and position. It began to disappear in 5 or 6 minutes after he had discovered it, 

 without changing its situation. The manner in which it vanished was quite irre- 

 gular ; large patches in different parts, and o{ different dimensions, ceasing to be 

 luminous, till the whole had disappeared. The evening was rather cloudy. 



4 L 2 



