222 DKSTllOVKRS OF SCHMEllOED WOOD — MlJRl'HY. 



" In lar^e rivers (to which the " Narrows '' may be compared) the 

 bottom velocity is much leas than the surface velocity. Du Buat 

 gives an approximate rule for finding the mean and bottom velocity 

 thus : — If a he the surface velocity, h the bottom velocity and y the 



mean velocity, all in inches per second, then b = {. ya — l) and 



y — 1 ^ et + ( f/a— 1)'). According to this,if the surfacevelocity 

 at the "Narrows" is 2| miles per hour, the bottom velocity will be 

 0.85 miles per hour and the mean velocity 1.54 miles per hour. 

 ■• I think we may conclude that in a current having a bottom 

 velocity of about 3 miles per hour, the operations of the Limnoria 

 would be much retarded, if not wholly prevented." 



