A SINGULAR 13 
gree as it paffes the prefent fhell of incumbent earth, and 
break it in fome places, as in earthquakes? And may not 
the progrefs of fuch wave, and the diforders it occafions 
among the folids of the fhell, account for the rumbling 
found being firft heard at a diftance, augmenting as it ap- 
proaches, and gradually dyingaway as it proceeds? A cir- 
eumftance obierved by the inhabitants of South-America 
in their laft vreat earthquake, that noife coming from a 
place, fome igprees north of Lima, and being traced by 
enquiry quite down to Buenos Ayres, proceeding regular- 
ly from NorthtoSouthat the rateof—Leagues per minute,. 
as | was informed by a very ingenious Peruvian whom. 
1 met with at Paris. 
EE 
NS Ve 
Explanation of a fingular phenomenon, firft obferved by Dr. 
FRANKLIN, and not hitherto fatisfactorily accounted 
for. Ina Letter from Mr.R. PATTERSON, to Dr. B. Rusu. 
Sar re 
Read O&. REMEMBER, feveral years ago to have read, 
pijeritt in one of Dr. Franklin’s philofophical tracts, 
an account of a fingular phenomenon, obferved when a 
veflel, containing oil and water, is put in motion—Thus 
ifa glafs tumbler, for inftance, about two thirds filled; 
with equal parts of water and oil, be moved gently back- 
wards and forwards in the hand; or, fufpended by a cord, 
be made to fwing like the pendulum ofa clock, the fur- 
face ofthe water in contact with the oil, which floats up- 
on it, will be thrown into a violent wave-like commotion, 
while the upper furface of the oil will be comparatively 
placid and even. 
The Doétor obferves, that having fhewn this experi- 
ment toa number of ingenious perfons, * thofe who are 
but 
