1811.] On a Luminous Arch seen in the Sky. SC3 



in that part of the west of England which lies opposite the Irish 

 Sea, to those in the west part of the south of Scotland, and to 

 those in the middle part of the west of Ireland. During the time 

 of its appearance the air was apparently still, and so clear that 

 more stars were visible than can be generally observed in star-light 

 eights. 



This phenomenon was a part of either a body of dense light, or 

 a mass of luminous matter, in the shape of an arch ; whose curva- 

 ture was considerably greater than that of the earth, but whose 

 middle part was flattened into a horizontal line, for a distance which 

 is equal to half the length of the visible part ; and whose direction, 

 when 1 rirst saw it, was N. 80 E'. and S. 80 W. The colour of 

 this arch, which was greyish white, resembled very much that of 

 the white parts of the clouds when the sun shines upon them. Its 

 lustre was weak. Its light, when I saw it, was not so intense as to 

 illuminate the air, except in its immediate vicinity; where the 

 light, as I am informed, extended to ihe ground, and probably as 

 far in every other direction : and it was so transparent that through 

 the western part stars of the first and second magnitudes could be 

 seen ; through its middle part, those so small as the third rate were 

 dimly seen ; and through its eastern part, those to the fourth rate 

 were just visible ; while the stars contiguous to both sides of it, to 

 the fourth magnitude, were very distinctly seen. 



The figure of the arch was in general well defined : but in a few 

 places near the lines which joined together its sides it appeared to 

 be softened by being mixed with the air, like a light-coloured cloud 

 just before it gives out rain. Such softened parts appeared for a 

 small time in tvi tain situations, then disappeared; and afterwards 

 others did the same in other situations. These appearances took 

 place occasionally when 1 saw the arch : and they were owing, I 

 suppose, to the gradual separation of small portions from the great 

 body of luminous matter. 



After the surprise had subsided which was excited by this object's 

 appearance, 1 made every observation in my power to ascertain its 

 dimensions and distance from the earth, and 1 soon acquired every 

 necessary particular for these purposes, except its distance from me. 

 To obtain this distance 1 had not then the means; but a week alter 

 its appearance 1 observed a paragraph in the Lancaster newspaper, 

 in which it was said to have " extended from the west across the 

 meridian to the N. K. by E. soon after eight o'clock." The time 

 at which my observations commenced must have been so near that 

 time that 1 proceeded in my calculations immediately alter reading 

 thh paragraph. 



The straight line between me and the eastern extremity of the 

 view was S. 60 E., and that between me and the western extremity 

 B. 77 tV.j so that the visible part of the Hrch subtended an angle 

 of H)7°. Now as I was ¥] miles N. 1 1 \\ . from Lancaster; by 

 conceiving a line whose; direction is S. 60 l'i. and N. 60 W ., or the 

 direction of the arch at the time of observation, to be drawn uuo»s 



