JOLTRNAL OF THE JOINT COMMISSION. 



51 



ascertained by more than 97 oL^ervations. The tangent to the parallel 31° 20' was ascertained 

 and produced in botli directions, cast and west, and the ordinates to the curve of the parallel 

 established. The coincidouco between the new tangent and the old ou^^. produefni from Ojo del 

 Perro, was satisfactory ; after making the necessarjallowanoe for tlie difterenco of ordinates, tlie 

 error was found to be only a few feet. The tangent west was produced aoroeg the level of tlie San 

 Luis valley and the Guadalupe Pass. In the mean time, a new observatory was erected at f^an 

 Bernardino springs, and the latitude obtained with the same instrument, and nearly the same set 

 of stars, was ascertained to be 31° 19' 4u'^38 by 57 observations. A third tangent was produced 

 east and west, that east being found to correspond and verify the second tangent. This last tan- 

 gent, being the third, was, on account of the absence of water, produced as far as the liills west of 

 the San Pedro. "While this was progressing, the astronomical party established itself to the north 

 of Santa Cruz, on the river of the same name, and the latitude of the point wa:: ascertained to 

 be 31° 17' 5C".33, from 73 observations. From this, a point on the parallel 31° 20', due north, 

 was ascertaiued by direct measurement, nnd a fourth tangent obtained, as In all the preceding 

 cases, by elaborate raeasuremeuts of the elongations of Polaris. An Rpprchinsif-ii w;4S enter- 

 tained that the third tangent^ by reason of its great prolongation, sometimes, as in passing tho 

 Guadalupe mountains, running over rough country, might prove crooked ; hut the verification 

 by means of the fourth tangent was complete, showing the greatest probable error of either 

 tangent, a distance of only 15 or 20 feet. 



A chronometric reconnoissance was then made to the westward, and it was ascertained that 

 the nearest durable water to the intersection of the meridian of 111 degrees west of Greenwich, 

 and the parallel of 31^ 20', was at Los Kogales. At this point was established an observatory. 

 The transit and zenith instruments were both mounted ; and the result of 120 observations 

 with the latter, and observations during two lunations with the first, gave for the latitude 

 31"^ 21' 00".4S, and longitude 110° 51' 02". 10 west of Greenwich. From observations at this 

 observatory a fifth tangent was deduced, and extended by a separate party in both directions, 

 running westward until the 111th meridian of lon;;itude was reached. Owin?: to the difficulties 



Q , _ -"O 



of the country, the longitude was transferred by direct measurement and by triangulation. 



Before this was concluded, a despatch was received giving the joint result of the Mexican and 

 United States parties, of the latitude and longitude of the initial point on the Colorado river. 

 ^Vith these data the azimuth of the line westward was computed to be G9° 19' 45", 9, and laid off 

 by measurements from the elongation of Polaris. 



This left nothing to be done but to trace the line and complete the topography between tho 

 111th and the Colorado, and the dispositions made for that are all embraced in the convention 

 between Senor Jimenez and myself, and Senor Jimenez and Lieutenant Michler, to which your 



r 



approval has Lc^n given. 



Major Emory, the American commissioner, further stated, that in reference to the instru- 

 ments used, and the methods employed in obtaining results, Mr. Salazar, the Mexican commis- 

 sioner, from long experience, was familiar with the mode adopted by both commissions, and it 

 was therefore not necessary to enter into particulars — the notes would show for themselves ; 

 but he begged to remind Mr. Salazar that they had discussed hefore, the subject of longitude, 

 and it was agreed between them, that in all determinations of longitude by the moon and 



moon 



culminating stars they should tate the Greenwich ephemeris, and not await the publi- 

 cation of the corresponding observations made at Greenwich, as at this distance it would 

 necessarily involve a delay of eighteen months or two years — a result clearly not contemplated 



