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fun to fink beneath the vifible horizon to the north- 
well, it being very clear in that quarter, except fome 
thin clouds a little above the horizon, which were 
painted of fine red and golden colours, as is ufual 
when the fun fets in a calm clear evening. But 
about 20 minutes after fun-fet, as near as I could 
judge, it then being darkifh, I was greatly furprifed 
to fee an Iris in the dufky air, at a height greater 
than is feen at any time in the rainbow. It was in 
the contrary quarter of the heavens to the fetting fun, 
and fell on the fmoke, mills, and evening vapours 
arifing from the city of London and its neighbour- 
hood. The arch feemed to be a full half circle, 
tho’ its lower parts fell fome degrees fhort of the 
horizon. It was very diftindtly feen for about i y 
minutes. Its colours the fame as in the rainbow, 
but fainter. The lower ends of the bow arole gra- 
dually higher from the earth, as the fun declined 
beneath the horizon, until the whole arch difap— 
peared. The center of the arch was above the ho- 
rizon at its firll appearance. What moft perplexed 
me, was, to find the caufe of this painted arch. I 
could not believe, that it proceeded from the lun- 
beams falling on rain ; for there had been none that 
afternoon ; nor was there any fort of figns of rain 
or rainy clouds to be feen ; the wind being northerly, 
and the air cool, and lomewhat hazy in the quarter 
where the bow appeared ; which was not near fo 
bright as the rainbow appears to be in the day-time ; 
and I believe, that it would not have been vifible at 
all in the prefence of the fun. I imagine it was 
formed on the grofs particles of the evening vapours, 
mixed with thofe of the fmoke arifing from the 
town ; 
