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XVI. Account of a luminous Appearance in the Heavens. By 
Mr. Tiberius Cavailo, F. R. S. in a Letter to Sir Jofeph 
Banks, Bart. P. R. S. 
Read April 5, 1781. 
I TAKE the liberty to fend you an account of a luminous, 
appearance obferved lad: night in the heavens, which feems 
to be very fingular in its nature, and quite didintf: from the 
aurora borealis. 
At about half an hour pad nine yefterday evening, being the 
27th of March, a wrhite light began to be feen in the iky, which 
became gradually more and more denfe till ten o’clock, at which 
time it tormed a compleat luminous arch from ead to wed. 
Of this I have been informed by others ; but at a quarter pad: 
ten 1 went out of the houfe and obferved it myfelf. At that 
time it appeared to be an arch of about ieven or eight dep'rees in 
breadth extended from ead: to wed:, or, as fome of my friends 
imagined, in the direction of ead: by north to wed by fouth. 
Its wedern part quite reached the horizon ; but the eadern part 
of the arch feemed to begin at about 50° or 6o° above the hori- 
zon. It did not pafs through the zenith but at about 8° or io° 
fouth ward of it, audit was nearly perpendicular to the horizon. 
1 he whitenefs of this arch was much denier than that 
any aurora borealis I ever obferved, though it did not cad fo 
much light upon the terredrial objects. Towards the middle 
it was fo denfe, that the dars over which it paffed were 
1 eclipfed ; 
