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XXX. An Account of the Earthquake felt in 
the IJland of Madeira, March 31, 1761: 
By Thomas Heberden, M. D. F. R. S. 
Communicated by William Heberden, 
M. D. F. R. S. 
Read May 21, TN the city of Funchal, on the ifland 
l?6u X °* Madeira, March 31, 1761, we 
were alarmed with the fhock of an earthquake, pre- 
ceded by the ufual noife in the atmofphere, like heavy 
carriages paffing haftily over rough pavements. It 
began at thirty-five minutes after eleven o’clock in 
the morning, and lafted (by my watch) full three 
minutes ; the vibrations, which were very quick, 
remitting and increafing twice very fenfibly, during 
the fhocks, which feemed to be progreffive, from 
eaft to weft. It has feparated fome rocks in the 
eaftern part of the ifland, which have fallen from 
the cliffs into the fea. It has likewife damaged the 
walls of feveral buildings : among the reft, my houfe 
has buffered, the ftone-walls thereof, which are two 
feet thick, being fplit in feveral places, which has 
happened in particular to the walls, which ftand in a 
direction north and fouth. 
During the earthquake, the fountain of this city 
(whofe water is very clear at other times) ran turbid 
and whitifh. 
The fea was agitated very fenfibly, fluctuating fe- 
veral times between high-water and low-water mark. 
The fluctuation of the fea continued longer in the 
eaftern parts of the ifland, than in this part. 
X 2 Though 
