[237] no 



All these circumstances tended, in a singular manner, to contract the ex- 

 tensive region between the Mississippi and the iVlissouri ; so that there was 

 not (so to speak) room for the intermediate territories which 1 had explored. 

 But my astronomical observations have, throughout, restored order. The 

 Missouri being thrown over to the west, and the Mississippi to the east, 

 while, at the same time, the latitudes are generally increased, each interme- 

 diate country has found its natural place. 



In fine, the Mississippi may be said to be now well known, I give, in 

 the Table ot Geographical Positions, already referred to, the numerous po- 

 sitions by which u is determined ; not that the lower part enters into my 

 map, but because these positions form a complete system in regard to this 

 majestic river — one of the most magnificent in the world, and even also 

 now one of those whose course is astronomically the best determined from 

 its embouchures to its very source. 



I return now, in relation to the m.ap, to the problem of the longitudes ; 

 which here, as everywhere else on the earth, demands numerous observa- 

 tions, against which a war-cry will continually be heard among geogra- 

 phers, as long as in their works of exploration they are restricted to chro- 

 nometric methods, lunar distances, eclipses, and other phenomena of rare 

 occurrence, without being provided with the ample means which science 

 can indicate, but cannot furnish, except when national governments con- 

 tribute by an allowance of both time and funds. In this aspect, I look upon 

 it as my duly to expose here the elements which have served in the deter- 

 mination of the principal longitudes of my map; so that observers who 

 may follow me over the ground it covers, may know where to direct their 

 efforts for improving these first results. 



When the calculations of the astronomical observations in which we 

 were engaged were a little advanced, I detached Lieutenant Fremont to 

 commence the construction of the map — charging myself with the calcu- 

 lation of the remaining observations, the long and tedious discussion of the 

 longitudes, and the computation of the meteorological observations which 

 I had brought together for determining the altitudes of the stations above 

 the sea. 



It was necessary for us, in the outset, to have some positive meridians 

 as well known as possible. In this regard, 1 had been fortunate enough to 

 have observed some occultations of fixed stars, and also the solar eclipse of 

 the 18lh of September, 1838. The reverend Mr. Verot had the kindness 

 to make for me the calculation. But at this period I had not been able to 

 procure the particulars of corresponding observations, nor the errors of the 

 tables as to the epochs of these phenomena. I was obliged, therefore, to 

 employ the elements for the calculations as they were given in the Nautical 

 Almanac. However, as the results could not be so much in error as to affect 

 sensibly the exactness of the construction of the map, I did not hesitate to 

 adopt them for the concurrent determination of the longitudes, which I 

 especially wanted. 



At a later period I had the pleasure to make acquaintance with Mr. S. 

 C. Walker, of Philadelphia, a distinguished astronomer, whose zeal and 

 industry are efficaciously contributing to the progress of astronomy in 

 the United Slates. Mr. Walker had taken the pains to form an extensive 

 catalogue of all important astronomical phenomena which have been ob- 

 served at different times in North America. He has progressed far in 

 the discussion and the reduction of the observations upon occultations 



