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LETTER X. 
An Account of the Agitation of the Water at Roch- 
ford in Effex, Nov. i, 1755, in a Letter frojn the 
Re^'cerend Air, Thomlinfon to the Rev. Dr. Sykes, 
, D. D. Dean of Burion. Com?nimkated by Tho. 
Birch, D. D. Secret. R. S. 
Chriflmas-Day, 1756. 
Read March II, will furprile you to hear, that we 
s ^ ■ X ^ome fymptoins of an earthquake 
at this place, on the very fame day, and about the 
fame hou’, in which the late dreadful convulfion of 
the earth was in fo particular a manner fatal to Por- 
tugal. One inftance of it was of a pond in a clofe 
of Mr. Sly’s, adjoining to the church-yard; where 
the water was obferved by Mr. Sly himfelf, to flow 
a confiderable way up the mouth of the pond, and 
then returning, to flow up the oppofite fide, repeat- 
ing this fort of motion for about a quarter of an 
hour. What is further remarkable in this cafe is, 
that, at the very time of this fluduation, Mr. Sly 
had the curiofity to examine the condition of two 
other ponds, which are but a fmall didance from 
the former, and found them both very flill and quiet. 
It may deferve notice, that the motion of the water 
in Mr. Sly’s pond was only from ead to wed, and 
from wed to ead, alternately. Whether the fludua- 
tion in thofe other ponds, which have been men- 
tioned in the news-papers, was the fame, it may be 
worth while : it will at lead be a matter of curiofity 
to inquire. Mr. Sly’s pond is very large, and almod 
round 
