and from 1/25 to 1/7, respectively. The form of these waves 

 can not be represented by a sine curve. For waves of moder- 

 ate height the form closely auproaches the trochoid, that is, 

 the curve which is described by a point on a disc which rolls 

 below a flat surface (fig. 3). Waves of great height deviate 

 froiu the trochoid; the troughs are wider and flatter and the 

 crests narrower and steeper. The wave form becomes unstable 

 when the ratio H/L equals 1/7. 



LINE ALONG WHICH DISC ROLLS 



Figure 3. Profile of a trocholdal wave (full-drawn 

 lines) and of a sine wave (dashed lines) . 



The wave velocity increases v/ith increasing steepness (in- 

 creasing values of H/L) , but the increase of velocity never 

 exceeds 12 Der cent. 



The water particles move approximately in cir cles, the 

 radii of v.'hich decrease rapidly with depth. The particle 

 velocity is not uniform but is greatest when the oarticles 

 are near the top of their orbit (moving in the direction of 

 wave progress) , with the result that the particles upon com- 

 pletion of each nearly circular motion have advanced a short 



8 



