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men of Lisbon when about to return into the river, 
{if they faw before them too great a furf upon the 
bar, which they apprehended might fill their boats 
in pafling) to empty a bottle or two of oil into the 
fea, which would fupprefs the breakers, and allow 
them to pafs fafely : a confirmation of this I have 
not fince had an opportunity of obtaining. But dif- 
courfing of it with another perfon, who had often 
been in the Mediterranean, I was informed that the 
divers there, who, when under water in their bufinefs, 
need light, which the curling of the furface inter- 
rupts by the refractions of fo many little waves, 
let a fmall quantity of oil now and then out of their 
mouths, which riling to the furface fmooths it, and 
permits the light to come down to them. — All thefe 
informations I at times revolved in my mind, and 
wondered to find no mention of them in our books 
of experimental philofophy. 
At length being at clapham where there is, on 
the common, a large pond, which I obferved to be 
one day very rough with the wind, I fetched out a 
cruet of oil, and dropt a little of it on the water. I 
faw it fpread itfelf with furprizing fwiftnefs upon the 
furface ; but the effedt of fmoothing the waves was not 
produced j for I had applied it fir ft on the leeward 
fide of the pond, where the waves were largeft, and 
the wind drove my oil back upon the fhore, 1 then 
went to the windward fide, where they began to 
form ; and there the oil, though not more than a tea 
fpoonfu), produced an inftant calm over a fpace fevtral 
yards fquare, which fpread amazingly, and extend- 
ed itfelf gradually till it reached the lee fide, making 
all that quarter of the pond, perhaps half an acre, 
as fmooth as a looking- glafs. 
Vol. LXIV. M m m 
Afte 
