PART 11. 



OBSERVATION'S. 



Office of the United States Naval Astronomical Expedition, 



Washington, D. C, June 29, 1854. 



Sir : I beg leave to submit herewitli the results of my observations, made beti^een Santiago 



de Chile and Montevideo, for the determination of geographical positions, elevations above the 



sea-level, and the magnetic elements ; and, in connexion therewith, to present a statement of 



the manner in which they were obtained, and the amount of reliability to be attached to them. 



OF THE LATITUDE. 



The altitudes were invariably measured with a sextant and artificial horizon, and, as the 

 sun's meridian altitude was too great for the sextant, the latitude has been generally derived 

 from double altitudes — there being two or more determinations for each place. 



In the months of November and December, during which these observations were generally 

 made, the sun passes too near the zenith in the parallel to which my work was confined for 

 very accurate determinations; but, from the close agreement of the results, I consider them 

 sufiiciently reliable for all practical purposes. 



Mendoza, for example, was found to be in 32° 50' 51" by two altitudes. 



51 18 " " 



51 21 " " 



50 45 " " 



51 07 by meridian altitude of moon. 



Mean 

 + 



32 51 04 latitude of hotel. 

 11 



South 32 51 15 latitude of Plaza. 



These results, however, agree more closely than the generality of them. 



OF THE LONGITUDE. 



On my first trip across the country I had three pocket-chronometers, only one of which was 

 of the least value for the determination of longitudes ; and on two occasions, although I wound 

 the others, I neglected to wind that particular one. Having no known position from which to 

 determine its error, and not time enough to ascertain definitively a position, I, of course, could 

 not rely on it. Moreover, I made the mistake of marking time by it at all observations, and, 

 by the necessary shifting from hand to pocket, vitiated its rate. I have, therefore, rejected all 

 chronometric determinations of the first journey, except that at the Casucha de la Cumbre, at 

 which place I did not stop on my second expedition. In this instance, taking the rate from the 

 Alto de la Laguna to the Casucha de los Puquios, according to their positions as determined on 

 the second journey, there is only to be considered a rate for about fifty hours, and, conseq[uently, 

 no probability of great error. 



On the return to South America, I was better provided, and had more experience. In addi- 



