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Received November 1 8, 1766. 
XIII. Some Obfervations on Swarms of Gnats , 
particularly one feen at Oxford, Auguft 
20, 1766. # Letter to Charles Morton, 
M. D. Sec . F. aS'. the Rev . John Swin- 
ton, 5 . jD. F. F. * 9 . Member of the 
Academy degli Apatifti at Florence, and 
of the Etrufcan Academy of Cortona in 
Tufcan y. 
Dear Sir, 
Read Feb. z6,r-r^ppE gnats have been more numerous,, 
176? ' J- as well as more noxious, here, during 
the months of July, Auguft, and September, 1766, 
than perhaps they were ever known to be before in the 
memory of man. So many myriads of them have 
fometimes occupied the fame part of the atmofphere, 
in contiguous bodies, that they have refembled a 
very black cloud, greatly darkened the air, and almoft 
totally intercepted the folar rays. The repeated 
bites iikewife of thefe malignant infeds have been 
fo fevere,. that the legs, arms, heads, and other 
parts,' affeded by them, in many perfons, have been 
fwelled to an enormous fize. The colour alfo of 
thefe parts, at the fame time, was red and fiery, 
perfedly fimilar to that of fome of the moft alarming 
inflammations. '* . 
. • As the natural hiftory of thefe troublefome infeds is 
fufliciently known, having been given us,. with great 
accuracy 
