252 Scientific Proceedings, Royal Dublin Society. 



wave-form has its surface wholly raised above the level of repose of 

 the fluid. This is what I mean to express by calling this wave 

 wholly positive. . . . The wave-proper of the first order is wholly 

 positive." {lUd. 340.) 



" The wave of the second order is partly positive and partly 

 negative, each height having a companion hollow, and this is the com- 

 monest order of visible water-wave, being similar to the usual loind- 

 waves, in which the surface of the water visibly oscillates above and 



below the level of repose " [Ibid. 317.) 



Mr. Russell distinctly asserts that ordinary sea-waves of the 

 second order become, on certain occasions, entirely transformed into 

 waves of his first order. He writes : — " After a wave has first 

 been made to break on the shore, it does not cease to travel, but 

 if the slope be gentle, the beach shallow and very extended (as it 

 sometimes is for a mile inwards from the breaking point, if the 

 waves be large), the whole inner portion of the beach is covered 

 with positive waves of the first order, from among which all waves 

 of the second order have disappeared. This accounts for the 

 phoenomenon of breakers transporting shingle and wreck and other 

 substances shorewards after a certain point; at a great distance 

 from shore, or where the shores are deep and abrupt, the wave is 

 of the second order, and a body floating near the surface is alter- 

 nately carried forward and backward by the waves, neither is the 

 water affected to a great depth ; whereas nearer the shore, the whole 

 action of the wave is inwards,^ and the force extends to the bottom 

 of the water, and stirs the shingle shorewards ; hence the abrupt- 

 ness also of the shingle and sand near the margin of the shore where 

 the breakers generally run." [Ibid. p. 373.) 



The results arrived at by Mr. Eussell as to the nature of his 

 wave of the first order were obtained by means of a series of 

 elaborate experiments ; but the above conclusions as to the con- 

 version of waves of the second order into those of the first order 

 seem to have been based on an insufficient number of general obser- 

 vations that were not brought to the test of experiment. 



^ According to Mr. Eussell the waye may assume this character before it breaks : — 

 " He must undoubtedly attribute the greatest moving power to the greatest depth of 

 water, because the largest and most powerful wave would thus be created, and before 

 they broke they would exercise the greatest amount of mechanical power to lift and 

 convey the shingle." (R. 63.) 



