316 REPORT— 1844. 



the visible effect is like that of an agitated sea. The waving motion visibly 

 travels across the whole length of the field, but the corn remains rooted to 

 the ground ; this illustration is as apt as old, being given to us in the Iliad, 

 at the conclusion of the speech of Agamemnon, beginning ^Q, (piXoi, ijpuyes 

 Anvaot. 



"iis (paro' .... 



KivijdTi h' dyoprj, ws Kv/xaTa fiuKpd da\da<rr)s 

 rioi'Tov 'iKcipiow, Tfi fiey t Ewpos re Norof re 

 "Uipop', eTTdi^as Trarpos Aios sk recpeXawv. 

 £i.v c ore KiPtjirei Ze<j)vpos jjativ Xrjioi', eXOioy 

 Adppos, enaiyii^toi', eni t i/fxvei darajf^veaaiv' 

 ' Lis rijjy wda dyoprj KiyijOi], — II. II. 144— 149. 



In the examination of the phasnomena of waves, we have therefore two 

 classes of elements for consideration, the elements of the wave motion and the 

 elements of the water particle motion. We may first examine the phcsnomena 

 of a given wave-motion, its range of transmission over the surface of the fluid, 

 the velocity of that transmission, the form of the elevation, its amplitude, 

 breadth, height, volume, period. We may next consider the joa^A which each 

 tvater particle describes dui'ing the wave transit ; the form of that path, the 

 horizontal or vertical range of the motion, the variation of the path with the 

 depth, the relation of e&cYi phase of the particles orbit to each portion of the 

 corresponding wave length. By this examination I have found that there 

 exist among waves groups of phaenoraena so different as to suggest their di- 

 vision into distinct classes. I find that the general form of waves is manifestly 

 different, one kind of Mave making its appearance in a form always wholly 

 raised above the general surface of the fluid, iind which we may call a posi- 

 tive wave, and so distinguisli it from another form of wave which is wholly 

 negative, or depressed below the plane of repose, while a third class are 

 found to consist of both a negative and a positive portion. I find them 

 propagated with extremely different velocities, and obeying different laws 

 according as they belong to one or the other of these classes, the positive 

 wave having in a given depth of tvater a constant and invariable velocity, 

 'while another class has a velocity varying according to other peculiarities, 

 and independent of the depth. Some of them again are distinguished by always 

 appearing alone as individual waves, and others as companion phcenomena or 

 gregarious, never appearing except in groups. In examining the paths of the 

 water particles corresponding differences are observed. In some the Mater 

 particles perform a motion of translation from one place to another, and efliect 

 a permanent and final change of place, while others merely change their place 

 for an instant to resume it again ; thus performing oscillations round their 

 place of final repose. These waves may also be distinguished by the sources 

 from which they arise, and the forces by which they are transmitted. One 

 class of wave is a motion of successive transference of the whole fluid mass ; a 

 second, thepartial oscillation of one part of it without afl'ecting the remainder ; 

 a third, the propagation of an impulse by the corpuscular forces which deter- 

 mine the elasticity of the fluid mass; and a fourth, by the capillary forces 

 uniting its molecules at the surface. 



These classes, so various both in their origin, cause and phsenomena, have 

 not hitherto been sufficiently distinguished, but have either been unknown, 

 or have been confounded with each other under the vague conception and 

 general designation of wave motions. The following table is given as a first 

 approximation towards a classification of the phcBnomena of tvave motion. It 

 comprehends all the waves which I have investigated, and sufficiently di- 



