( 862 ) 



From this table we derive for the proportion between the computed 

 average velocity for the whole of the wet section to the velocities 

 observed clown to 6 M. in the middle of the widened part of the 

 canal, the following values : 



at high water How at ebb (low 



f from the Red Sea) (towards the Red Sea 



1.17 1.45 



1.47 1.40 



1.43 1.30 



1.40 liU 



Moan 07 1.44 



The true value of this proportion for the case in which observation 

 and computation agree, is unknown, Hut if we consider that the floats 

 went down to only 6 M. below the surface whereas the depth of the 

 water at Hood tide was over 8.50 M. and at ebb time over 7.50 M. 



and furthermore, that the canal had side slopes of 1 vertical on 27 a 

 horizontal, we conclude that at all events the velocity in the middle 

 must have considerably exceeded the average velocity for the whole 

 of the section. As far as can be ascertained therefore, the formula 

 applied to the Suez-Canal leads to results which do not clash with 

 the observation. 



More conclusive information cannot lie derived from a comparison 

 of the computed velocities to the observed values. As long therefore 

 as complete observations, made for the widened Suez canal, concerning 

 the relation between the velocity of the current, the tidal motion and 

 the dimentions of the section, have not furnished us with more reliable 

 information about the value of the coefficient and about the question 

 whether the formula applies fully to the case, we cannot avoid a 

 relatively considerable uncertainty in the calculation of the maximum 

 velocity. 



§ 5. A closer examination is therefore required to decide in how 

 far the velocity of the current in an open canal may cause a hin- 

 drance to navigation and whether this hindrance cannot be overcome. 



In discussing this question we must consider, on the one hand that 

 the computed velocities represent average velocities for the whole of 

 the wet section and that therefore the absolute velocities in the 

 middle of the canal will be more considerable; on the other hand, 

 however, that the computed velocities are relative to the greatest 

 possible differences in the height of the tide. The computed maximum 



