( 858 ) 



leads tó a velocity <>t' propagation of 10.06 M., whereas we find 

 9.54 M. by observation. 



Matters stand somewhat differently for the third supposition. The 

 formula by which the velocities of the currents are computed is the 

 well known formula for permanent uniform motion. It is in the 

 nature of the thing that such a motion cannot occur in a canal where 

 a strong tidal motion takes place. But the question on which every 

 thing depends is not so much this, whether the use of this formula 

 leads to sufficiently correct velocities for any moment, as the following, 

 whether the computed maximum velocities are not too small. 



In reference to this question we may remark that in general the 

 formula will lead to too small a value of the velocity during the 

 period that change in level is accompanied by decrease of inclination ; 

 to too great a value where the change is accompanied by an increase 

 of inclination. 



If, taking this into consideration, we examine the parts of the 

 canal K.M. 0—9 and K.M. 9—27, during the period of 4 1 /, to (5 

 hours after low tide on the Pacific, we get as follows : 



Time elapsed Mean inclination 



since low tide K.M. 0—9 K.M. 9— '27 



4J hours 



0.000044 0.000040 

 0.000048 0.000046 



0.000048 

 0.000044 



1 1, ui Mil )47 

 0.000045 



From these data it appears that, during the half hour preceding 

 the epochs at which the velocities reach their maximum value at 

 K.M. 9 and 27 the mean inclination for the part 0—9 as well as 

 for the part 9 — 27 has been little variable but increasing. 



From this it follows that by the application of the formula at these 

 epochs we probably cannot have made any important error. 



Meanwhile, in order to test the validity of the computations, we 

 have still to inquire whether the computed velocities, taken in con- 

 junction with the computed levels, satisfy the equation of continuity. 



dl dv dl 



dt dx dw 



where / represents the area, v the mean velocity of the wet section 

 at the distance x from the Pacific, at the epoch t. 



