VOL. XXXII.] PHILOSOPHICAL TRANSACTIONS. t)23 



interval between the former and middle comet would be 81 years, and between 

 the middle and last comet 162 years, so that the revolution of the comet 

 would be 81 years, and the history of other comets would also agree very well 

 with these. 



Concerning the Appearance of several Arches of Colours, contiguous to the inner 

 Edge of the common Rainbow, observed at Pelworth in Sussex, by the Rev. 

 Dr. Langwith. N° 375, p. 241. 



When the primary rainbow has been very vivid, I have observed in it, more 

 than once, a second series of colours within, contiguous to the first, but far 

 weaker, and sometimes a faint appearance even of a third. These increase 

 the rainbow to a breadth much exceeding what has hitherto been determined by 

 calculation. 



I have since observed something of the same nature, though not in the same 

 degree of perfection, with the above. On March 22, 17^2, a little before 6 

 in the evening, wind at N. W. by W. we had here a lively, distinct, primary 

 rainbow, the inner and purple colour of which had a far greater mixture of red 

 in it than I could ever observe in Sir Isaac Newton's oblong spectrum. Under 

 this was a space, of a breadth considerably less than that of the limbus of the 

 rainbow, in which I could not distinguish any colours; still lower was a faint 

 interrupted arch of red, inclining to purple, which appeared and vanished 

 several times, while 1 was observing it. 



March 27, 1722, in the evening, about a quarter before 6, wind S. W. we 

 had one of the finest rainbows I ever beheld. The first series of colours was 

 as usual, only the purple had a far greater mixture of red in it than I had ever 

 seen in the prismatic purple ; under this was a coloured arch, in which the 

 green was so predominant, that I could not distinguish either the yellow or 

 the blue: still lower was an arch of purple, like the former, highly saturated 

 with red, under which I could not distinguish any more colours. 



The order of the colours in this compounded rainbow was, you see, red, 

 yellow, green, blue, a mixture of purple and red, green, or rather a mixture 

 of yellow, green, and blue, a mixture of purple and red. 



August 21, about half an hour past 5 in the evening, weather temperate, 

 wind at N. E. the appearance was as follows, viz. The colours of the primary 

 rainbow were as usual, only the purple very much mclining to red, and well 

 defined; under this was an arch of green, the upper part of which inclined to 

 a bright yellow, the lower to a more dusky green ; under this were alternately 

 two arches of reddish purple and two of green; under all a fjiint appearance of 

 another arch of purple, which vanished and returned several times so quick, 



