[ 6 7 2 ] 
Church of St. Martins in the Fields , very fenfibly 
felt the Bed heave, and confequently the Earth mult 
heave too. There was a hollow, obfcure, rufhing 
Noile in the Houfe, which ended in a loud Explo- 
fion up in the Air, like that of a fmall Cannon : 
The whole Duration, from the Beginning to the 
End of the Earthquake, feemed to be about 4 Se- 
conds of Time. The Soldiers who were upon Duty 
in * 5 V. James's Park , and others who were then up, 
faw a blackilh Cloud, with confiderable Lightning, 
juft before the Earthquake began; it was allb very 
calm Weather. 
In the'Hiftory of Earthquakes it is obferved, that 
they generally begin in calm Weather, with a black 
Cloud. And when the Air is dear, juft before an 
Earthquake, yet there are then often Signs of Plenty 
of inflammable fulphureous Matter in the Air; tuch 
as Ignes Fatui or Jack- a- Lanterns, and the Me- 
teors called falling Stars. 
Now, I have fhewn many Years flnee, in the Ap- 
pendix to my Statical EJJays, Experiment 3. Page 
280. the Effect that the Mixture of a pure and ful- 
phureous Air have on each other; viz. by turning 
the Mouth downwards, into a Pan of Water, of a 
Glafs Vefiel of a Capacity fufficient ro hold about 
two Quarts, with a Neck about twenty Inches long, 
and two Inches wide. Then, by putting under ir, 
in a proper Glafs Veflel, with a long narrow Neck, 
a Mixture of Flqna fortis , and powdered Pyrites, 
viz. the Stone with which Vitriol is made, there 
will be a brisk Ferment, which will fill the Giaf^ 
with redifh fulphureous Fumes ; which, by generating 
more Air than they deftroy, will caufe the Water, 
with 
