I 237 ] 98 



With these two barometers, as well before as after my excursions in the 

 west, I compared those which were for use in my journeys. Unfortunate- 

 ly, we were not able to compare the two between themselves directly at the 

 epoch when the care of making the observations passed from one hand to 

 another, as 1 have already mentioned ; nor for the subsequent reductions 

 am I able to say which of the two instruments was more reliable than the 

 other, or that either was entirely to be considered as what is called a stand- 

 ard barometer ; although, in relation to my travelling barometers, they have 

 been both necessarily so regarded, respectively. 



The two series observed, as I have indicated, and makiiig use only of 

 the noon readings, have served for me to deduce the elevation of St. 

 Louis above the Gulf of Mexico. It must be remarked, however, that 

 the aggregate of the observations, independent of what has already been 

 said, is not numerous enough to assure the exactness of an element so 

 delicate as the mean annual heiglu of the barometer. Experience proves 

 that many years of observations are required for that. The absolute 

 elevation, therefore, which I have assigned to St. Louis in the table, will, 

 probably, hereafter have to be amended. It may be that the absolute 

 height of the barometer, by which it is implied, is uncertain, to at least 

 0.050 inch, and that the effect of the error is to make the altitude too 

 high. 



As for some time the members of the Western Academy have under- 

 taken a regular system of meteorological observations, we have reason to 

 hope that, in some years from this, there will be a definite clearing up of 

 this point. Then the correction, which turns out proper to be applied to 

 the altitude of St. Louis, will be also applicable, in the same sense, to all the 

 altitudes of the table which are north of the mouth of the Ohio. The rela- 

 tive differences of level will remain the same ; only the absolute level above 

 tide will be changed. 



When the course of my observations carried me to the regions of the 

 north and northwest, the stationary barometer at St. Louis, to which my 

 portable barometers were referred, became too distant for simultaneous ob- 

 servations to be any longer comparable. I had foreseen this difficulty, and 

 had succeeded in establishing, as soon as needed, two new fixed barometer 

 stations, much higher north— the one at St. Peter's on the Mississippi ; 

 the other at Camp Kearney, near Council Bluffs, on the Missouri. At 

 each of these points there was a stationary barometer, corresponding four 

 or five times in the day with the barometer at St. Louis, and affording, 

 at the same time, for my portable barometers, a reference to one or the 

 other, according as my position at any time brought one or the other the 

 nearest. 



Nevertheless, as both of these stations are at a great distance from St. 

 Louis, whether the length of the journey necessary for communicating 

 between them, or their geographical positions and direct distance apart, be 

 considered, it became necessary that their differences of level, as respects 

 St. Louis, should be determined by the greatest number of observations 

 possible. In this view, I deem it fit to introduce here the results of these 

 determinations. 



\. The station at Cawp Kearney was occupied by the venerable mis- 

 sionaries, the Rev. Messrs. De Smedt and Werreydt. I furnished them 

 with a barometer, well compared with that of Dr. Engelmann at St. 

 Louis, and with my own, and delivered it at thdr missionary station in 



