( 863 ) 



velocities may occur therefore only on a couple of days every year. 

 And on these days only during a few hours. 



In how far a relatively rare velocity of the current oilers diffi- 

 culties to navigation is of course ascertained in the best way by a 

 comparison to canals on which under similar conditions similar 

 velocities occur. For such a comparison the Suez-canal offers the 

 best conditions. For this canal several observations about the velocity 

 of the current are known. Published observations, however, cannot 

 lay claim to completeness, at least not for the present purpose. In 

 the first place because they have not been frequent enough to justify 

 the belief that among them will have occurred these rare cases which 

 by an unfavourable coincidence of circumstances, must have given rise 

 to exceptionally great velocities. In the second place because the 

 measurements are, as a rule, relative to absolute velocities in the 

 middle of the canal and not to the average velocity for the whole 

 of the wet section. 



Moreover, in comparing the Panama-canal to the Suez-canal we 

 have to consider that the dimensions of the former will be much 

 more considerable than those of the latter as originally executed. 

 Consequently such velocities as have caused no difficulties for the 

 Suez-canal will cause them still less for the Panama-canal. 



For the Suez-canal between the Bitter Lakes and Suez originally 

 had a bottomwidth of 22 M. and a depth of 8 M. below mean 

 springtide low water, with which dimensions corresponds a cross 

 section of 330 M s . On the other hand the sea level Panama-canal 

 would get a bottomwidth of about 45.7 M. (150 feet) and a depth 

 of about 12.2 M. (40 feet) corresponding with a cross section of 

 855 M 2 . 



Observations, made during the period 1871 — 1876, have brought to 

 light the following facts about the velocities of the current in the 

 Suez-canal between the Bitter Lakes and Suez. l ) 



"The maximum velocity of the high water flow, running North- 

 "ward, amounts to 0.80 to 0.90 M. at the springtides of the months 

 "of May and November, to 1.15 — 1.35 M. p. s. in the months of 

 "January and February. 



"The maximum velocity of the ebb flow running Southward amounts 

 "to 0.75 — 0.80 M. at the springtides of the months of May and Novem- 

 "ber, to 1.20 — 1.25 M. p. s. in the months of July and August. 



"Along Port-Thewlik in the canal south of the main channel 



i) Vide the paper of Mr. J. F. W. Conrad pp. 89 and 90. 



59 

 Proceedings Royal Acad. Amsterdam. Vol. IX. 



