216 



Mr. A. Tylor on Tides and Waves, 



and prevent the tide-gauge ever registering the tidal influences 

 alone at any point. This is the cause of different establishments 

 at neighbouring ports apparently in similar position as regards 

 the luni-solar influences. 

 ¥ig. 1 shows that the area of the gap formed when the wave 



Fhna 



F.M Lines of horizontal forward motion of particles with vertical motion. 



V.M Lines of vertical motion of particles without horizontal motion. 



B.W1 Lines of hof?;zontal backward motion of particles with vertical motion 



was generated is the limit of horizontal movement of particles 

 throughout the run of that wave. Experiments show that if 

 waves artificially produced for experiments continue the same 

 height their velocity diminishes, and if their height diminishes 

 they may keep up their velocity. It is impossible to keep up 

 both the velocity and height of any wave a long distance. If it 

 were possible it would involve perpetual motion, as the wave is 

 resisted by the air above. and by the water in which it vibrates. 

 Let v represent velocity of the motion of a wave measured in 

 feet and the time (a second) in which its crest passes a fixed point, 

 and p the depth of the water in feet ; then by means of the for- 

 mula v=3\/p the actual velocity found by experiment may be 

 predicted as accurately as by the usual formula v = \/gh*. The 

 latter formula appears extremely incorrect for great depth, as it 

 indicates impossible velocities for waves. If the depth of the 

 Atlantic was 21,952 feet, the greatest velocity that could by any 

 means be given to a wave would be 84 feet per second, or 58 

 miles per hour; for if was \^Sp, then from this we have 

 84=3v/21952, that is, 84 feet per second is the maximum ve- 



* The gravity formula, v 2 —2gJi, only applies where there is no resistance 

 to motion. It is of no use in cases of uniform motion. My new formula 

 (page 205) gives the due effect of weight on velocity. Thus in a river or 

 a glacier with sixty-four times the quantity (or weight) flowing or sliding, 

 the velocity would increase four times at the same slope. This law ex- 

 plains why in the glacial period frozen rivers reached such low levels, and 

 why denudation was so large in the pluvial period, as destructive effect is 

 in a high ratio to the velocity. 



