[ 237 ] 106 



contains 165 altitudes, the elements of which consist of not less than 10,000 

 barometric and thermometric readings ; and if to these be added what I 

 caused to be observed at various points, to serve for comparison and redac- 

 tion, we shall not come short of OU,0UO meteorological observations, which 

 have had to be availed of in some sort, for this particular, in the geographi- 

 cal positions I present. 



The astronomical observations have been made with different sextants. 

 The one most commonly used is of a kind known under the name of Hopp^s 

 improved sextant, and having a radius of nine inches. Others of six-inch 

 radius, occasionally employed, came from the shop of Mr. Troughton. 1 

 was provided with two chronometers ; one of which, by Brockbank, espe- 

 cially, has preserved, for two years, a rate truly striking, if one considers 

 the difficulties of the region we had to explore. 



The observations of the campaigns of 1838 and 1839 were made by 

 Lieutenant Fremont and myself; Mr. Fremont counting the chronometer 

 and reading. But, in the year before, during which I explored the 

 sources of the Mississippi and the adjacent regions, being without an as- 

 sistant, I had to answer by myself for every part of the observation ; and 

 as the stations were constantly at the junction of rivers, or on the shore of 

 some lake, it would be difficult for me to describe what I had to undergo, 

 from wet, from insects, and from want of an organization proper to favor 

 my work. 



The elements of the celestial bodies observed, as they were needed 

 for the calculation, were taken from the "Nautical Almanac;" and the 

 calculation of this considerable mass of astronomical observations has been 

 executed by Lieutenant Fre nont and myself, aided for three months by 

 Lieutenant E. P. Scammon, corps of topographical engineers, whose zeal 

 and intelligence on this occasion, as well as the talent with which he has 

 assisted Lieutenant Fremont in the construction of the map, insures my 

 gratitude. 



The reconnoissance of the country traversed each day, or rather the 

 survey of our route, by land or by water, was made by taking the mag- 

 netic bearing of every point, by estimating its distance, and by making, 

 as we went, a connected sketch or bird's-eye view of the whole, and very 

 often including distant points of importance indicated to us by the guides, 

 to which one of us always went to take note of. This part of the labor I 

 assigned to liieutenant Fremont ; and his co-operation during 1838 and 

 1839, while it left me more time to spend upon other duties, as the chief 

 of the expedition, proved also otherwise advantageous, by the talents 

 which he displayed for this branch of service, and the activity and ac- 

 curacy v;hich have always characterized whatever he has had occasion 

 to perform under my directions. There has been no exception to this 

 arrangement, unless under some particular circumstances, or in cases 

 where, to gain time, we were divided into two parties, to explore different 

 districts. So, in 1838, while I was making the reconnoissance of the 

 beautiful region to which I have given the name of Undine, Lieutenant 

 Frdmont was employed upon that of the [\'azi-oju river, (riviere aux 

 Embarras of the French,) which falls into the Mississippi seventeen miles 

 below lake Pepin, and which I supposed then to be a river that would 

 play an important part in some treaty with the Indians, which the gov- 

 ernment appeared to project. So, too, in 1839, while we were going up 

 the Missouri, in order not to lose the advantage presented to us ia th« 



