40 
Mr. Pennant also mentions an observation of the like nature made by the 
seal-catchers in Scotland (Brit. Zool., Vol. iv.—Article, ‘Seal.’) When these 
animals are devouring a very oily fish, which they always do under water, the 
waves above are observed to be remarkably smooth; and by this mark the 
fisherman know where to look for them. 
(Note by Dr. Brownrigg. ) 
Sir Gilfred Lawson, who served long in the Army at Gibraltar, assures me 
that the fishermen in that place are accustomed to pour a little oil on the sea in 
order to still its motion, that they might be able to see the oysters lying at its 
bottom, which are there very large, and which they take up with a proper 
instrument. This Sir Gilfred had often seen performed, and said the same was 
practised on other parts of the Spanish coast. 
(Extract from a Letter of Dr. Franklin to Dr. Brownrigg. ) 
London, November 7th, 1773. 
Dear Sir,—I thank you for the remarks of your learned friend at Carlisle. 
I had when a youth, read and smiled at Pliny’s account of the practice among 
seamen of his time, to still the waves in a storm by pouring oil into the sea, 
which he mentions, as well as the use made of oil by the divers ; but the stilling 
of a tempest by throwing vinegar into the air escaped me. 
Perhaps you may not dislike to have an account of all I have heard, and 
learnt, and done. 
In 1757, being at sea in a fleet of ninety sail bound against Louisbourg, I 
observed the wakes of two of the ships to be remarkably smooth, while all the 
others were ruffled with the wind. I pointed it out to the captain, and asked 
him the meaning of it. ‘The cooks,’ says he, ‘have, I suppose, been just 
emptying their greasy water through the scuppers, which has greased the sides 
of those ships a little.’ 
Afterwards being again at sea in 1762, I first observed the wonderful quietness 
of oil on agitated water in the swinging glass lamp I made to hang up in the 
cabin. An old sea captain then a passenger with me, thought little of it, 
supposing it an effect of the same kind with that of a little oil put on water to 
smooth it, which he said was a practice of the Bermudians when they would 
strike fish which they could not see if the surface of the water was ruffled by 
the wind. The same gentleman told me he had heard it was a practice with 
the fishermen of Lisbon, when about to return into the river, if they saw too 
great a surf upon the bar, to empty a bottle or two of oil into the sea, which 
would suppress the breakers, and allow them to pass safely. Discoursing of it 
with another person who had often been in the Mediterranean, I was informed 
that the divers there who, when under water in their business, need light, 
