36*2 ON THE MOTION OF WAVES. 



spreading themselves over the surface of the water. This experi- 

 ment will not succeed in a bason or other small vessel full of water, 

 wherein the particles of oil have not room enough to expand them- 

 selves. 



If a heavy body be dropped on the surface of water which is thus 

 covered with a film of oil, the waves will take place in the same 

 manner as if there were no oil. But the blowing of the wind will 

 have little or no effect upon it. In this case the oil seems to act be- 

 tween water and air, in the same manner as it acts between the mov- 

 ing parts of mechanical engines ; viz. it lubricates the parts, and 

 renders the motion free and easy. 



But whether this be the real explanation or not, the fact is not 

 less true than surprising ; and a very useful consequence has been 

 derive.! from it, namely, a method of stilling the waves of the sea in 

 certain cases. 



It is expressly mentioned by Plutarch* and Pliny f, that the sea- 

 men of their times used to still the waves in a storm, by pouring oil 

 into the sea. But since the revival of learning, though several ob- 

 servations relative to it are to be found in accounts of voyages, &c. 

 yet I do not know that any notice has been taken of this account by 

 any philosophical writer, previous to the late celebrated Dr. Frank- 

 lin, who collected several accounts relative to the subject, and made 

 a variety of experiments upon it, the sum of which is as follows {. 



A small quantity of oil, for instance, a quarter of an ounce, will 

 spread itself quickly and forcibly upon the water of a pond or lake, 

 to the extent of more than an acre ; and if poured on the windward 

 side, the water will thereby be rendered quite smooth as far as the 

 film of oil extends, whilst the rest of the pond may be quite rough, 

 from the action of the wind. 



If the oil be poured on the leeward side, then the force of the 

 wind will, in a great measure, drive it towards the bank. Besides 

 which, the experiment is frustrated by the waves coming to that side 

 already formed ; for the principal operation of the oil upon water is, 

 as it seems, 1st. to prevent the raising of new waves by the wind; 



* Qiuest. Nat. f Hist. Nat. lib. ii. c. 103. 



^ See his paper on the stilling of waves by means of oil, in the Phil. Tran. 

 vol. Ixiv. or in his Miscellaneous Papers. 



