The Port Gibson herald, and correspondent., 1850-08-23
U The following is from pamphlet written
and published BY Professor Forshey;
MEMOIR ON THE PHYSICS or THE
MISSISSIPPI RIVER.
BY CALEB G. FoRsaEY. A. NJ

BY CALEB G. FoRSAEY, A. NJ, c. E.
/. Rate Of Fail -FrorKthe mouth Of the river
to a point 400 miles up its tortuous channel, is
distance in right line Of only 220 miles, Its
length is nearly double the right line distance.
For 800 miles above New Orleans, it NAV. for
practical purposes, he regarded as twice the dis
tance Of the right line.
2. The mean depth Of the river at high water
mark is not materially different at Natchez from
Carroton, though nearly 800 miles apart.
section Of the river at CarrolIton, made at high
water Of 1849, is l65,260 square feet: and at
Nldalla, Opposite Natchez,) the section is l67-
600 feet The bottom Of uniform channel 400
miles up, is about on level with The bar at the
Southwest Pass. The rate of fall is not uni-
| form on the surface. but decreases in decivty
towards the Gull, giving a curve Of inclination
(probably parabolic) to which the Gulf level is a
tangent, at tin Balize. The mean rate Of decli-
nation is 80 inch pr mile, FOR the first hundred
miles. 200 inches the second hundred, 9 80
inches for the third. and 57inches for The fourth
/ hundred miles. Above this point have no ac-
curate data bat am inclined to think that the rate
is not materially different, 10 the upper extreme
Of the delta above the mouth ofthe Ohio. These
data relate to high water.
g. The low water curve or declivity has a
mean descent Of "a inch per mile for the first
hundred lies, and so, .83, 20 inches for the
next consecutive three hundred miles; making
the Total difference of level 2l.I feet from point
ten miles above Natchez, to the BaIize.
4. These rates are not uniform for short dis
! tances, interrupted as the channel is by many
short bends which arrest the currents regular
i flow, and make series of comparative levels
| and falls in the surface current The means
obtained are from levels made Of segments Of
the channel, 25 28 l6 and ! 90 miles in length,
and are, think, reliable. They are, at least,
| the best data within my knowledge.
5. Depth Of Water.-Within the 400 miles
/ treated. the depth of the river at high water is
not materially different. Near Natchez found
an extreme depth Of 1873 feet. and like depth
has been found at several points in the vicinity
| Of New Orleans.
| One depth of 1877 feet was recently found
near Shrewsbury, about ten miles above the city.
These are extreme cases. When the chan
4 mel is distant from both shores, 1875 feet is the
usual maximum. A section made in front of
| Vidaia half a mile below the Natchez ferrV
gave mean depth of sos feet, with maxi
mum Of about 100; and like section Of high
water channel at Carrollton gave mean depth
of II .6 feet. The low water depth may always
be obtained by snbstracting the range from the
high water. At Vidalia, the range is 81 feet;
and at Carrollton 5 feet. The mean depth of
the low water sections would then be 295 feet
and 56 feet.-And the sectional areas at low
water give 1900 square feet for Carrollton,
and 10000 at Vidaia.
6. The channel continues TO maintain great
depth down to point very near the debouchure.
How near, I know not but certainly beyond the
head of the passes. At Fort jackson it is SO
feet deep, and point midway down the South
i West Pass was found l02 feet.
/ z. Widh.-The uniformity of breadth in the
channel is remarkable feature Of the Missis-
sppi river. great number Of measurements
made by myself, from the Balze to Gasena. l.
/ 700 miles up the river, give mean width, IN
cIuding wide places in the bends of about 1000
wards; excluding these 500 yards; and the upper
portion of this is wider, including expanses
produced BY bends and islands, than 1000 yards;
but excluding them they are the same The
addition of the four great rivers below, make
no increase in the breadth Of the river The
Missouri at Bonneville, 300 miles above its
mouth, fonnd half mile wide.
1t appears from these facts relating to the
width OF the Mississippi that it does not follow
the law Of continent streams, as given in the
books. We sbali have occasion to see that in
many other features it is a river sui generis.
g. Velocity Of Currents.-To obtain the sur
face velocity of the river, | have established
parallel sights, transverse to the river, and with
an assistant, at one Of the stations, timed float
ing drih-woud on still days. at all parts Of the
surface, estimating by the eye their distance
from shore. This have done at all stages of
water, and derived the mean o! each set, TO the
number of many hundreds Of observations.
g. The result shows mean surface velocity
at high water OF 26l miles per hour, at Carroll
ton, and 2 so miles per hour at Vidaia; respect
lively, $50 and 3.82 feet per second of time
The one was derived from l76 observations, and
| the other from 10 observations. At low water,
Carrollton. AS miles per hour. or I'll feet per
second at Vidalia, l.54 miles per hour, or 2. .25
feet per second.
To- The mean velocity for mean water, as
derived from thirty years observation, is 2.26
miles per hour, or 2.95 feet per second.
IL. The velocities at various depths are not
easily obtained. The Irregularities of bottom
and sides in the channel, and their continually
shifting nature, give so many lateral and vertical
directions to portions Of the current, as very
much to equaize the current velocity, at all
dep.hs. Besides, the largeness Of the volume