ASTRONOMY. 



175 



C. 



lomical observations for estciblisldng the WWi meridian of longitude icest of G 

 for determining the parallels 31° 47' and 31*^ 20' north latitude : By John H, 



The four manuscript volumes wliicli have been suhmitted to the U. S. Commissioner, emhrace 

 a complete tabulation of all the observations, both for latitude and longitude, made along the 

 parallels of 31° 47' and 31° 20'. It will be seen, by a reference to these volumes, that each of 

 the stations has been determined in latitude with a zenith telescope, (T. & S.,) by about one 

 hundred observations, and two in longitude, with a transit of thirty-six inches focal length, 

 by observations on the moon and moon culminating stars. 



In accordance with the direction of the Commissioner, the stars for latitude were at first 

 selected exclusively from the Greenwich Twelve-year catalogue. At Espia, however, it was 

 found that this catalogue no longer afforded, in that portion of the heavens then observable, 

 a sufficient number of pairs that would fulfil the conditions required for satisfactory results. 

 It was therefore deemed expedient, in the exigencies of the survey, to rely subsequently almost 

 wholly upon the British Association catalogue. 



It was found, by combining the results of observations on about thirty pairs of stars talcen 



•m 



from this catalogue, that any error in the final result arising from errors of polar distances was 

 materially reduced ; and although, by comparing the means of the observations on each pair, 

 there seemed to be in some cases errors of polar distances developed, all the results were never- 

 theless incorporated to obtain the one adopted ; nor was a single observation rejected because of 

 its aijparent inconsistency or want of parallelism with any previous or subsequent result obtained 

 by it or by any other pair, except at one station, (Agua del Pe ro ) wliere the instrument was 

 mounted on a roct, (no timber being attainable,) and the observations otherwise rendered objec- 

 tionable by the violence of the wind. Thus the result of every pair, whether high or low, and 

 without reference to the '< general run," has been included in the ''means" used to obtain the 



latitude adopted. 



A subsequent and careful revision in the office of the computations made in the field has dis- 



closed no considerable error. 



A brief summary of the observations and results of all the stations, and a reference to the 



tables which are appended, are here given : 



1. The observations at Los Nogales for determining the 111th degree of longitude west of 

 Greenwich, extending through two lunations, and computed from data furnished by the IS autical 

 Almanac, gave the result as shown by Table I, 110° 51' 0r'.95, (7^ 23» 24M3). The latitude 

 deduced from 120 observations on 29 pairs of stars, taken from the British Association cata- 

 logue, is (see Table II) 31° 21' 00".48. . . 



2. Seventy-three observations on 23 pairs of stars, selected from British Association catalogue, 

 give for the latitude of the station near the head of Rio Santa Cruz, (Table III) 31 17 5b .66. 



3. At San Bernardino there were 57 observations on 21 pairs from British Association cata- 



(Table 



97 



(Table Y) 



5. At Agua del Perro there were 81 observations on 25 pairs of stars selected from both cata- 



