ON WAVES. 341 



selves accurately graduated, the side of the channel opposite to the window 

 being covered with lines at distances precisely equal to those on the window 

 and similarly situated. These methods are the only methods of observation 

 I have found it useful to employ, but I have now increased the number and 

 variety of the observations sufficiently to enable me to adduce the conclusions 

 hereinafter following, as representing the phsenomena as far as their nature 

 will admit of accurate observation. 



It is characteristic of waves that the apparent motion visible on the surface 

 of the water is of one species, while the absolute motion of the individual par- 

 ticles of the water is very different. In reference to all the species of waves 

 this is true, both as regards the velocity and nature of the motion ; nevertheless 

 the one is the immediate cause or consequence of the other. In the case of 

 the wave of the first order, the visible motion of the wave form along the sur- 

 face of the water may be called the motion of transmission, the actual motion 

 of the particles themselves is to be distinguished as the motion of translation. 



We infer the motions of the individual wave particles from those of visible 

 small bodies floating in the water; any minute particle floating on the surface 

 will sufficiently indicate the motion of the water particles about it, and the 

 motion of deeper particles may be conveniently observed in the case of waves 

 of the first order, by using the little globules of wax already mentioned ; 

 these small globules may be so made as to float permanently at any given 

 depth, yet they will be visibly affected by very minute forces. 



In this way the following observations were made : 



Absolute Motion of Translation. — The phsenomenon of translation charac- 

 teristic of the wave of the first order, and which we have used as its distin- 

 guishing appellation, is to be observed as follows. Floating globules, as 

 already described, being placed in the fluid, and their positions being noted 

 with reference to the sides and bottom of the channel, let a wave of the first 

 order be transmitted along the fluid ; it is found that the effect of this trans- 

 mission is to lift each of the floating particles, and similarly, therefore, the 

 water particles themselves, out of their positions, and to transfer them perma- 

 nently forward to new positions in the channel, and in these new positions 

 the particles are left perfectly at rest, as in their original places in the channel. 



The measure or range of translation is just equal to that which would re- 

 sult from increasing the column of water in the channel behind the wave by 

 a given quantity, and diminishing the column anterior to the particles by the 

 same quantity, that quantity being equal to the volume of the wave. That 

 is to say, the range of translation is simply equal to the space in length of the 

 channel lohich the volume of the wave would occupy on the level of the water 

 in repose. 



The total effect of having transmitted a wave of the first order along a 

 channel, is to have moved successively every particle in the whole channel 

 forward, through a space equal to the volume of the wave divided by the 

 water-way of the channel. 



Parallelism of Translation. — If the floating spherules before mentioned be 

 arranged in repose in one vertical plane at right angles to the direction of 

 transmission, and carefully observed during transmission, it will be noticed 

 that the particles remain in the same plane during transmission and repose 

 in the same place after transmission. 



^ It is further found, as might be anticipated from the foregoing observa- 

 tions, that a thin solid plane transverse to the direction of transmission, and 

 so poised as to float- in that position, does not sensibly interfere with the 

 motion of translation or of transmission. 



Tfie Range of Horizontal Translation is equal at all Depths Vertical ex- 



