ON WAVE MOTION. 



407 



Then for surface rollers over the ocean, L miles long, and period 

 T hours, the velocity is K knots, given bj' 



(2) 

 (3) 



(4) 



27r 27rR 21600' 



L=KT, 



K G^ 



T 27rR' 



With the period given in t seconds, ^=3600 T, 



K_ 3600x 21600 . _ 3 / G V- 

 t G' 288 (,900/ ' 



making K=3^, if 17-= 289 is replaced by 288, near enough on the 

 accuracy of the numerical data ; and then 



(5) K=10800T, L==10800T-, K2=10800L. 



Measuring the length of the wave by I feet, six to the fathom, 



(6) 



K.=^^2^B=^l=l . 81 



6000 



For the long flat tidal waves through the depths of an ocean h fathom 

 deep, the formula to employ is 



(7) 



with 



(8) 



^'=^i^^o= E mo' ''' ^'^'' 



G = 17x900, R=3438, 4=sin l' = 0-00029, 

 /i=0-0147K-, K=8-2oVh; or K=Gs//, 



for a depth the fraction /of the radius of the Earth. 



Thence a table for ocean tidal waves, where the result is given to the 

 nearest round number. 



H H 2 



