ON THE MISSISSIPPI. 19.'* 



Let A B (Plate V. Fig. 1.) represent the longitudinal section 

 of a river flowing with uniform velocity from surface to bottom, 

 and let us enquire what change ought to take place in the ve- 

 locity at different depths, caused hy the pressure of the fluid: 

 Let us suppose a wall C D, forming a complete transverse sec- 

 tion of the river, and moving uniformly with the current from 

 A, to B, and that the whole inferior part B, is instantaneously 

 removed; if now orifices be made in the wall at 1, and 2, the wa- 

 ter will flow out in the direction of the stream, with velocities in 

 the ratio of the square-roots of the columns ahove the respec- 

 tive orifices; upon this partial view of the subject, the theorists 

 have built their system. Again, supposing all things to remain 

 as before, the portion of the river B, being replaced, let us 

 now suppose the superior portion A, to be removed, while the 

 wall moves on uniformly with the current and portion B, if 

 now the same orifices 1, and 2, be opened, the water will flow 

 out with the same velocities as before, but in contrary direc- 

 tions, against the course of the river; hence it appears that the 

 simple pressure of the water is equally disposed to produce in- 

 ferior currents in any direction, the instant the equilibrium is 

 destroyed ; but it is certainly very unphilosophical to assert that 

 the column 3, 4, will produce an increased current in the di- 

 rection of the stream, while it is opposed by a column of equal 

 pressure 1, 2: it cannot be asserted that any inequality of pres- 

 sure, arising from the gentle declivity ot the surface of large 

 rivers, can produce any sensible effect ; for should it be said 

 that the pressing and opposing columns are not to be measur- 

 ed in contiguity to each other, but that the opposing column 

 will be null, in consideration that a point is to be found on the 

 surface of any river, upon the same level with any given depth 

 higher up the stream; we reply, that this effect is totally de- 

 stroyed by other concomitant circumstances. Great rivers whose 

 regimen is long established flow with a very gentle declivity, 

 perhaps in some cases not more than 2 inches per mile, but let 

 it be supposed one foot; according to the theory the velocity of 

 an inferior current a b, (Fig. 2.) at the depth of 16 feet a c, ought 

 to be 32 feet per second, because at the point b, 16 miles be- 

 low c, there is no opposing column : this is certainly the most 



