( 870 ) 



Mean sea-level. 



nearly straight lines, and further that the velocity of propagation of 

 the tides is known with sufficient accuracy, likewise owing - to obser- 

 vations made on the Suez-canal. Therefore we will be able to 

 determine the difference of the velocities at 64 and 2«S K.M. distance 



I— I. 



from the Atlantic, for the epochs at which — - — is a small quantity. 



'M 



This will be the case near the moment of low water. 



For the difference of the velocities v 1 and r, during the half hour 

 preceding the moment of lowwater at K.M. 64, during which half 

 hour the velocity of the current will be maximum at that point, we 

 find as follows for spring-tide. We assume that between the distances 

 28 K.M. and 64 K.M. (from the Atlantic) there is a retardation of 

 the tides of just one hour : 



at x j, hour before lowwater : {v,— v) = 0.32 M. -f 0.02 v 

 „ lowwater : (v— v) = 0.12 M. -f 0.015 v. 



From these figures it appears, that during the half hour before 

 lowwater at K.M. 64 the differences of the velocities of the current 

 are only to a small extent dependent on the value of the velocity v. 

 These differences, therefore, may be determined with sufficient pre- 

 cision, even if the velocity v is only approximatively known. 



By observations made on the Suez-canal during the period 1871 — 



