664 TRANS. OF THE ACAD. OF SCIENCE. 
than low water at the mouth of the Ohio, as given in the same 
table 
The data for Mr. Nicollet’s calculation were his own baro- 
metrical levellings all along the Mississippi river, and obser- 
vations made here by the Rev. Mr. Van Sweevelt of the St. 
ouis University and by myself. The data about the level 
of localities in St. Louis, and especially about the low water 
mark, he received from the late Mr. R. Paul, then city engi- 
neer, who had assumed it to be 28 feet 6 inches below the 
City Directrix,} or 2 feet higher than subsequent experience 
(especially during January, 1840) proved it to be. It is 
therefore necessary to subtract this amount from his 382 feet, 
which gives us 380 feet as the altitude of our present low wa- 
ter mark, : 
Dr. A. Wislizenus next calculated the elevation of St. Louis 
above the Gulf. His results are published in his Report on 
a tour to Northern Mexico, printed by order of the U. 8. Sen- 
ate, in 1848, p. 140. He found, by comparing his observa- 
tions made at the seashore near the mouth of the Rio Grande 
with the cotemporaneous ones made by me here, the altitude 
of the City Directrix (which by mistake is stated to be 38 ft. 
1 inch instead of 30 feet 6 inches above low water) to be 420 
feet, which will bring the altitude of low water to 389 feet 6 
inches. ; 
Desirous of verifying these results, I availed myself in De- 
cember, 1853, of the kind offers of assistance of the late Prof. 
Edw. H. Barton of New Orleans, and transmitted to him one 
of my barometers, which he compared with his instrament 
during more than four months, from January 3 to May 
1854. The barometer sent, E. 2., ranged 0.080 inches lower 
t+ The top of the curbstone at the intersection of Market street and on 
Levee is called the City Directrix, to which point all the elevations in 
ci 
found that this point was elevated 30 feet 6 inches above the lowest stage 
of the river experienced for many years, and it is so stated on 
water mark is 7 feet 7 inches above the City Directrix, and 38 feet 
above low water. The Mississippi river had only once, since th orable 
tion of the city, risen to a similar height, viz. in April of the mem 604 
“Année des grandes eaux,” 1785. From some indefinite data in oe shal 
lection of the oldest inhabitants, it was supposed that the river Mert 0 is 
even a foot or so higher than in 1844. The low water mark 0 
the one now considered as the correct one. ere 
¢ What a glorious addition to our knowledge of the configuration 0 
; : ; itution 
North American continent would it be, if the Smithsonian as aude 
ters of all observers carefully compared, so that accurate calc ; 
the altitudes of each could be made. By connecting these aia ol pet 
e railroad surveys extending over the whole country, ble ; a ie 
results would be obtained. -It is hoped that the plan proposed by 
