496 THE POPULAR SCIENCE MONTHLY. 



So much for the practical effects of oil on broken water. Now 

 let us proceed to examine the reasons why so small a quantity of 

 oil can produce these effects. In order to understand the methods 

 for opposing the violence of waves, it is essential that the phe- 

 nomena which constitute wave motion be understood. It can be 

 said with some degree of confidence that there is no instance in 

 Nature of a perfectly quiescent surface of water. Air and water 

 are both mediums of extreme mobility, and the individual mole- 

 cules of both, and of all other substances, are continually in a state 

 of motion, with different velocities, in paths different in direction 

 and length. There is thus a continual interlacing of particles. 

 When air covers water, some of the particles of air, in their ex- 

 cursions, strike the surface of the water, producing unequal press- 

 ures upon it, and giving rise to ripples which the vision is not 

 acute enough to detect. If the original surface of the water were 

 perfectly smooth, and if all parts of it continued equally exposed 

 to an equal wind, waves could not be produced. But with the mi- 

 nute corrugations which are always present upon the smoothest 

 water it is to be observed that it does not occur that water is all 

 equally exposed to equal winds. The pressure of moving air upon 

 the crests and posterior portions of the minute corrugations is 

 greater than that on the hollows and anterior portions. There is 

 thus a tendency to heap up the water at the places of greatest 

 pressure, which is augmented by the rotational or vortex motion 

 produced by the viscosity of the air. These actions produce new 

 forms and inequalities, which, exposed to the wind, generate new 

 modifications of its force and give rise to further deviations from 

 the primitive condition of the fluid. Imagine an isolated example 

 in which the water has been suddenly heaped up by a gust of 

 wind. The action of gravity causes the particles of water in the 

 he.ap to push forward the particles immediately in front of them 

 out of their former place to another place farther on, and they 

 repose in their new place at rest as before the original heaping up. 

 Thus in succession volume after volume continues to carry on a 

 process of displacement which only ends with the exhaustion of 

 the displacing force originally impressed and communicated from 

 one to another successive mass of water. As the particles of 

 water crowd upon one another in the act of going out of their old 

 places into the new, the crowd forms a temporary heap visible on 

 the surface of the water, and as each successive mass is displacing 

 its successor there is always one such heap, and this heap travels 

 apparently at that point where the process of displacement is go- 

 ing on ; and although there may be only one crowd, yet it consists 

 of always another and another set of migrating particles. This 

 moving crowd constitutes a true wave. The velocity of the wave 

 is the velocity with which the heap is seen to move. Its form is 



