ON WAVES. 313 



1837). The resistance which the watei* in a channel opposes to the passage 

 of a floating body along that channel depends materially on the nature of the 

 great wave of the first order, which the floating body generates by the force 

 which propels it, and its motion is materially affected by the genesis of waves 

 also, of the second order, arising from the same cause. These wa^'es are 

 therefore important elements in the resistance of fluids, and acquaintance 

 with their phsenomenais essential to the sound determination and explanation 

 of the motion of floating bodies. If to these two branches of science we add 

 the useful arts, in which an accurate acquaintance with wave phaenomena 

 may be of practical value to the purposes of human life, we shall find that 

 the improvement of tidal rivers, the construction oi public works exposed to 

 the action of waves and of tides, and the formation of ships (see Reports of 

 Brit. Ass. passim), are among the most direct and necessary applications of 

 this knowledge, which is indeed essential to the just understanding of the 

 best methods of opposing the violence of waves, and converting their motion 

 to our own uses. By a careful study of the laws and phaenomena of waves, 

 we are enabled to convert these dangerous enemies into powerful slaves. By 

 such applications of our wave researches, we therefore extend our knowledge 

 in conformity with the maxims of the illustrious founder of our inductive phi- 

 losophy, who enjoins that we always study to combine with our experimenta 

 lucifera such experimenta fructifera, that while science is advanced society 

 may be advantaged. 



The Nature of Waves and their Variety. 



When the surface of water is agitated by a storm, it is difficult to recog- 

 nize in its tumultuous tossings, any semblance of order, law, or definite form, 

 which the mind can embrace so as adequately to conceive and understand. 

 Yet in all the madness of the wildest sea the careful observer may find some 

 traces of method ; amid the chaos of water he will observe some moving forms 

 which he can group or individualize ; he may distinguish some which are 

 round and long, others that are high and sharp ; he may observe those that 

 are high gradually becoming acuminate and breaking with a foaming crest, 

 and may notice that the motion of those which are small is short and quick, 

 while the rising and falling of large elevations is long and slow. Some of the 

 crests will advance with a great, others with a less velocity ; and in all he will 

 recognize a general form familiar to his mind as the form of the sea in agita- 

 tion, and which at once distinguishes it from all other pheenomena. 



Just as the waters of a reservoir or lake when in perl'ect repose are cha- 

 racterized by a smooth and horizontal surface, so also does a condition of dis- 

 turbance and agitation give to the surface of the fluid this form characteristic 

 of that condition and which we may term the wave form. When any limited 

 portion of the wave surface presents a defined figure or boundary, which 

 appears to distinguish that portion of fluid visibly from the surrounding mass, 

 our mind gives it individuality, — we call it a ivave. 



It is not easy to give a perfect definition of a wave, nor clearly to explain 

 its nature so as to convey an accurate or sutficiently general conception of it. 

 Persons who are placed for the first time on a stormy sea, have expressed to 

 me their surprise to find that their ship, at one moment in the trough between 

 two waves, with every appearance of instant destruction from the huge heap of 

 waters rolling over it, was in the next moment riding in safety on the top of 

 the billow. They discover with wonder that the large waves which they see rush- 

 ing along with a velocity of many miles an hour, do not carry the floating 

 body along with them, but seem to pass under the bottom of the ship without 

 injuring it, and indeed with scarcely a perceptible effect in carrying the vessel 



