130 Ex, Doc, No. 41. 



PassOj and that he must have traveled south of that ridge, in an al- 

 most due west course to the Rio Colorado. 



I use the word ^^Sierra Madre'^ in the sense attach^ to it hy the 

 Mexicans, viz: that ridge which separates the waters that fall into 

 the Atlantic from the rivers which empty into the Pacific ocean, 

 without any regard to its elevation. 



I pray you to accept the assurances of my distinguished consider- 

 ation and personal regard. 



- Your most obedient and faithful servant, 



ALBERT GALLATIN. 



To Lieutenant W. H. Emory, 



U. S. Topographical ^ Engineers^ Washington. 



Wa 



Dear Sir: In answer to your letter of the 1st instant, I have the 

 ^pleasure to send you, with the permission of the chief of my de- 

 partment, a table of twenty-three geographical positions deteijmined 

 "by myself, which you are at liberty to use; and, should you thmk 

 the information of sufficient importance, I should feel much flat- 

 tered that you should, as you propose, communicate them to the 

 Ethnological Society of New York for publication. 



No astronomical observations that I am aware of have everbefore 

 been made on the same grounds, if we except the observations ot 

 Dr. Coulter at the mouth of the Gila, which have never yet been 



published. ^ x. A 



You will see that the position of the Gila is very much changea, 



as well as that of Santa Fe, in New Mexico. , 



The observations were made with an 8^ inch sextant, constructea 

 by the celebrated Gambey, of Paris. In most cases, the determina- 

 tions of the places in latitude are the mean of the results ob- 

 tained by many observations on north and south stars, of near j 

 equal altitudes, by which the errors of eccentricity, &c., in the in- 

 strument were avoided. _ - 



The longitudes are derived from a combination of the results n^ 

 the chronometers, and measurement of distances between the moo 

 and stars, nearly equi-distan.t on either side of it. , 



The chronometers used were two very good box chronometers, j 

 Parkinson & Frodsham, (Nos. 783 and 2,075.) \ Vk 



The observations themselves, including those between S^"*L. 

 and Fort Leavenworth, (our point of departure,) in number 2;5W;o^ 

 3 000 were all computed in the field, and are now undergoing veri- 

 ficatio'n by Professor Hubbard, a very accurate young computer, at- 

 tached to the observatory at Washington. 



The computations for all the points embraced in the table «en 



you, have been verified. _ 



The objects of our expedition being purely military, the subjeci» 

 of interest to scientific men ware only pursued so far as they wer^ 

 incidental to the expedition, and did not interfere with its great oo- 



