70 



OBSERVATIONS. 



tion to the Iwst of my former clironometers, P. & F. No. 1915, belonging to the government, I 

 luad Barraud No. 5I3, also belonging to government, and P. & F. No. 2683, of my own. 



Takin"- Rosario, on the Parana, as my initial point, and assuming its longitude as determined 

 by Captain Sullivan, R. N., in H. B. M.'s brig "Philomel," to be correct, I made as little 

 delay as possible in reaching Mendoza, my first terminal point, making observations at several 

 places on the road. The longitude of Mendoza was then determined by chronometric differences 

 with Santiago, in the following manner: 



The day of my departure from Mendoza, (December 6, 1853), and again on my return from 

 Santiago, (December 21, 1853), I made observations for clock error. This gave me one rate. I 

 also obtained observations in Santiago, on my first arrival from Mendoza (December 14, 1853), 

 and again on my last arrival (January 3, 1854), which gave me another rate. The longitude 

 of Santiago having been accurately determined by the observations of the "Expedition," I 

 worked back from December 14 and January 3, to Mendoza, December 6 and 21, with both 

 rates, and obtained the following results: 



Barraud. 



P. & F. 1915. 



P.& F.2683. 



Means. 



h.m. s. 



h.m. s. 



k. m. s. 



k. m. s. 



4 35 56.6 



4 36 05.7 



4 35 53.9 



4 35 49.2 



42.1 



35 39.0 



49.0 



4 35 50.3 



48.8 



35 51.2 



48.9 



4 35 48.6 



29.8 (a) 



35 45.2 



42.6 





4 35 44.3 



4 35 50.3 



4 35 48.6 



4 35 49.4 



Or, rejecting (n), 4/i. 35m. 49.2s. 



The last determination by Barraud is rejected; because, at the Estero de las Cruces this 

 chronometer slipped from my pocket, and, although it fell on the sand, the jar was sufficient to 

 alter its rate. 



The longitude of Mendoza being thus determined to my satisfaction, I adopted the rate 

 between that place and Rosario for all intermediate places ; and between Mendoza and Santiago 

 for stations in the mountains. 



lu order to judge of the amount of probable error in these determinations, I append the 

 Greenwich mean time as shown by each chronometer, (with errors applied) at those points on 

 the road where the greatest discrepancies existed : 



Villa de la Concepcion, November 16, 1853 — • 



Uspallata, December 26, 1853- 



It may be as well to remark, that I carried all three chronometers in a belt strapped around 

 my waist, and under my clothes. In this way they were kept at as near the same temperature 

 during the journey as was possiljle. 



As an additional proof of the accuracy of determinations of longitude by means of pocket- 

 chronometers, I beg leave to recall to your memory the fact that Mr. Mowatt, of Valparaiso, 

 determined the difference of longitude between Santiago and Valparaiso liy this means in Jan- 

 uary, 1852, and that this difference was found to agree, within a very small fraction of a second, 

 with our determination by electric telegraph in September, 1852. 



Besides the chronometric determinations, I had also determinations deduced from the begin- 

 ning and end of the solar eclipse of November 30, 1853; the observation of the end being very 



Barraud . 



. 7 35 12.0 



1915 . . 



. . 7 55 26.4 



2683 . . 



. 7 55 32.4 





h. m. s. 



Barraud . 



. 7 23 21.0 



1915 . . 



. . 7 23 26.4 



2683 . 



. 7 23 26.8 



