6i8 



SCIENTIFIC NEV\^S. 



[June 29, lE 



THE EFFECT OF OIL ON WAVES. 



IT is now somewhat over a century since Franklin 

 made his experiments on the effect of oil on the 

 pond at Clapham. His attention had been drawn to the 

 subject by noticing the smoothness of the sea around 

 some ships from which a quantity of greasy water had 

 been thrown, and in his experiments he found that a 

 teaspoonful of oil poured on the windward side of the 

 pond gave its previously ruffled surface a mirrorlike 

 smoothness. But Franklin's (observations were over- 

 looked until attention was called to the subject a few 

 years ago by articles and correspondence in Chambers's 

 Journal. Since then the subject has met with increasing 

 attention, and has been the occasion of reports from the 

 Royal National Lifeboat Institution, the U. S. Hydro- 

 graphical Office, and the English Admiralty, as well as 

 of a recent French work by Vice-Admiral Clone. 



When a drop of oil is placed upon a clean water surface it 

 spreads with great rapidity over a very large area, form- 

 ing a continuous film of extreme tenuity. A simple ex- 

 periment, which can be made by any one, will illustrate 

 this. Take a soup plate, which has been very carefully 

 cleaned and freed from grease by means of soda. Fill 

 the plate with clean water from the tap, and place the 

 plate in front of the window or a gas lamp, so that the 

 light may be reflected from its surface. A few specks 

 of dust will generally be seen floating on the water ; 

 watch one of these whilst a pencil or bit of stick, which 

 has previously been dipped into oil, is made to touch 

 lightly the surface of the water at its centre. The 

 moment the pencil touches the water the speck of dust 

 will be seen to fly off with great rapidity towards the 

 rim of the plate, being driven by the spreading film of 

 oil which has covered the whole surface of the water. 

 If now the pencil be again brought into contact with the 

 water so as to deposit a small drop of oil upon its sur- 

 face, this drop of oil will spread with comparative slow- 

 ness, showing as it does so the brilliant iridescent 

 colours due to the interference of light reflected from its 

 two surfaces, which, however, soon again disappear as the 

 film extends and becomes thinner. The thickness of the 

 oil film first formed is, in fact, far less than a wave length 

 of light (which itself lies between fifteen and thirty 

 millionths of an inch), being probably not more than a 

 fiftieth of this, or less than a two-millionth of an inch. 

 A single grain of oil would therefore cover an area of 

 fifty or sixty square feet or more. 



By the presence of such a film the phenomena 

 depending upon the surface action of the water become 

 materially changed, and it need, therefore, cause no sur- 

 prise that so small a quantity of oil should so greatly 

 affect the production and maintenance of those water- 

 waves, whose origin lies in the interaction of the air and 

 the water. When the wind blows over the sea with 

 sufficient force the friction between the wind and the 

 water causes the latter to be thrown into ripples, 

 whose propagation depends almost entirely on the 

 surface tension of the liquid, but with increased 

 velocity of the wind these ripples give place to true 

 waves, whose propagation depends on the gravitating 

 forces of the water, and whose velocity of motion 

 depends on the height and breadth of the waves and 

 the depth of the water. 



In ordinary water-waves, such as are produced by 

 movingthe hand up and down on the surface of Stillwater, 

 the commotion travels outwards with a certain speed as 

 an undulatory motion, in which the individual particles 



of the water only execute oscillations about their posi- 

 tions of rest, so that a cork floating on the surface of the 

 water simply moves up and down as the waves pass it. 

 Of a similar nature are the ordinary unbroken 

 waves seen on the surface of a bay during 

 fair weather. But when such a wave approaches the 

 shore and reaches the shelving beach, its character 

 changes. The impediment off'ered to the motion of the 

 wave by the friction with the ground beneath becomes 

 perceptible at some distance from the shore, and increases 

 as the wave advances into shallower water, with the 

 result that the form of the wave becomes more and more 

 steep towards the shore, until at last it curls forward, 

 and the upper part of the wave acquiring an onward 

 motion, it rushes up and breaks upon the beach. The 

 change, which in this way takes place in the character of 

 the wave from a simple symmetrical undulation to a 

 bodily onrush of the water, which is here caused by the 

 retardation of the lower portions of the wave, may also 

 result from an acceleration of the upper part of the wave 

 by the continued action of the wind. When a wave 

 after its formation is further acted upon by the wind, the 

 the effect is twofold ; firstl}', to increase the size of the 

 wave, and secondly, to change its form. The wind blow- 

 ing horizontally over the water exerts more action on 

 the crest of the wave than in the trough between, and 

 thus causes the wave to become more and more steep on 

 the leeward side, until at last its crest topples over and 

 breaks. It is thus that the " catspaws " are produced 

 when the sea is agitated by a rising wind, or the gusts 

 which precede a squall ; and in a larger but similar way 

 the comparatively harmless rolling ocean waves become 

 changed during a storm into thj destructive walls of 

 water which break with such terrific force upon the decks 

 of a ship. 



The trials which have been now made of the effect of 

 oil show quite clearly that not only can the thin ■ilm of 

 oil, interposed between the wind and the water, check 

 the formation of waves in comparatively still water, but 

 also, and in this lies its great utility, it can prevent the 

 formation of the great walls of water just mentioned, 

 the waves as they enter the oil-covered area passing 

 along as great swells upon which the ship rides in com- 

 parative safety. In this way even small boats have been 

 enabled to ride out for nearly three days a violent 

 cyclone, while moored to a raft of broken spars and 

 rigging to which bags of oil were fastened. 



For oil to be effective during a storm, it must be applied 

 so as to form an oil protected region extending from the 

 ship in the direction from which the waves advance. 

 This can be effected by letting the ship ride at anchor 

 with canvas bags, each containing a few pints of oil, 

 preferably of animal or vegetable origin, slung from the 

 anchor chain or a forward part of the ship ; or if the 

 ship be let drift before the wind, it is sufficient to let the 

 bags hang over the side, as the drifting of the vessel by 

 the wind will carry it into the protected area. A very 

 small quantity of oil suffices, five or six gallons being 

 ample for twenty-four hours, and it should be allowed to 

 trickle slowly from pricks in the bags, as a more rapid 

 flow only causes waste. 



In those cases where the breaking of the waves is due 

 not to the wind but to reefs or other obstacles below the 

 surface of the water, the action of oil is not so marked, 

 though even here it does some good. In the report of 

 the National Lifeboat Institution, while the benefit of oil 

 to ships in the open sea is acknowledged, it is concluded 



