ON WAVES. 



317 



stinguishes them from each other. I find that water waves may be distributed 

 iotofou?- orders. The wave of' tj'anslatioji is the wave of the first order, 

 and consists in a motion of translation of the whole mass of the fluid from one 

 place to another, to another in which it finally reposes ; its aspect is, a solitary 

 elevation or a solitary hollow or cavity, moving along the surface with a uniform 

 velocity ; and hence it presents two species, positive and negative, and each 

 of these may be found in a condition oi free motion, or affected in form and 

 velocity by the continual interference of & force of the same nature with that 

 from which its genesis was derived. The wave of the second order is partly 

 positive and partly negative, each height having a companion hollow, and this 

 is the commonest order of visible water wave, being similar to the usual loind 

 tuaves, in which the surface of the water visibly oscillates above and below 

 the level of repose ; these waves appear in groxips ; in some cases, as in run- 

 ning water, they may be standing elevations and depressions, and in others 

 progressive along the surface, and like the wa\'es of the first order, may be 

 altered in form and velocity by the presence of a disturbing force, so as to 

 difier from their phaenomena when in a state of perfect freedom. The third 

 CLASS are met with under such conditions as agitate the fluid only to a very 

 minute depth, and are determined by the same forces which in hydrostatics 

 produce the phaenomena of capillary attraction ; and the fourth order is 

 that wave insensible to sight, which conveys the disturbance produced by a 

 sonorous body through a mass of the fluid, and which is at once an index and 

 a result of the molecular forces which determine the elasticity of the fluid. 

 This classification has been adopted throughout the following paper. 



* Table I. 



System of Water Waves. 



Orders, i First. \ Second. Third. Fourth. 



Designation. iWave of translation. jOscillating waves. Capillary waves. Corpuscular wave. 



Characters...|Solitary. 

 I 



Positive. 

 Negative. 



Free. 

 Forced. 



Species . 



Varieties 



Gregarious. 



Stationary. 

 Progressive. 



Free. 

 Forced. 



Gregarious. 



Free. 

 Forced. 



Solitaiy. 



r The wave of resistance. Stream ripple. Dentate waves. Water-sound wave. 

 Instances ■< [The tide wave. Wind waves. Zephyral waves. ; 



L The aerial sound wave. Ocean swell. | I 



An observer of natural phaenomena who will study the surface of a sea 

 or large lake during the successive stages of an increasing wind, from a calm 

 to a storm, will find in the whole motions of the surface of the fluid, appear- 

 ances which illustrate the nature of the various classes of waves contained in 

 Table 1., and Avhich exhibit the laws to Avhich these waves are subject. Let 

 him begin his observations in a perfect calm, Avhen the surface of the water is 

 smooth and reflects like a mirror the images of surrounding objects. This 

 appearance will not be affected by even a slight motion of the air, and a ve- 

 locity of less than half a mile an hour (8^ in. per sec.) does not sensibly 

 disturb the smoothness of the reflecting surface. A gentle zephyr flitting 

 along the surface from point to point, may be observed to destroy the perfec- 

 tion of the mirror for a moment, and on departing, the surface remains polished 

 as before ; if the air have a velocity of about a mile an hour, the surface of the 

 water becomes less capable of distinct reflexion, and on observing it in such a 

 condition, it is to be noticed that the diminution of this reflecting power is 



