16 



THE TRANSATLANTIC LONGITUDE. 



same reticule had been very thoroughly and satisfactorily deduced from an ample 

 series of observations in 1860-61 at Pensacola, it appears that little would probably 

 be gained by an attempt to obtain additional data at Valencia. Indeed, after 

 assorting the thread-intervals deduced from the Valencia observations into three 

 classes, the accordance of the mean values for these classes showed a probable error 

 amounting for but few of the threads to so much as 0^02 of a great circle. 



The Pensacola values had been deduced from 121 transits of 21 stars, — the 

 average declination of 9 of them being 75|°. The probable error of but few of the 

 intervals was so large as 0^.005; and the combination of these values with those 

 derived from the Valencia observations gives all needful accuracy. The Pensacola 

 values were therefore reduced to the focal adjustment of the instrument at Valencia 

 by diminishing each interval by its three-thousandth part, and a triple weight was 

 assigned to the resultant values. 



We thus have, for the equatorial intervals of the several threads from the mean 

 of all, the following determinations : — 



Equatorial Thread-intervals of Transit No. 4. 





Pensacola values 











Valencia, 1866. 



Adopted value. 





18GO-61. 



Reduced to 

 Valencia focus. 







B, 



-1-34M56 



+ 34M45 



+ 34M17 



-f34M38 



B, 



31.784 



31.774 



31.834 



31.789 



Bs 



29.255 



29.245 



29.311 



29.261 



B, 



26.850 



26.841 



26.829 



26.838 



b: 



24.317 



24.309 



24.289 



24.304 



c, 



19.450 . 



19.444 



19.424 



19.439 



c, 



17.136 



17.130 



17.134 



17.131 



Cs 



14.574 



14.569 



14.570 



14.569 



c 



12.204 



12.200 



12.187 



12.197 



C5 



9.799 



9.796 



9.755 



9 786 



p. 



4.909 



4.908 



4 904 



4 907 



D. 



+ 2.456 



+ 2.455 



-f- 2 462 



-f- 2.457 



D, 



—0.034 



— 0.034 



— 0.038 



— 0.035 



D^ 



2.372 



2.371 



2 366 



2.370 



D, 



4,717. 



4.716 



4.750 



4.724 



E, 



9.677 



9.674 



9.693 



9.679J 



E. 



12.220 



12.216 



12.175 



12.206 



E, 



14.634 



14.629 



14.647 



14.634 



E, 



17.154 



17.148 



17.166 



17.152 



e: 



19.467 



19.461 



19.442 



19.456 



E, 



24.438 



24.430 



24.433 



24431 



e1 



26.858 



26.849 



26.837 



26.846 



Pa 



29.382 



29.372 



29.361 



29.369 



F, 



31.770 



31.760 



31.789 



31.767 



E5 



—34.168 



—34.157 



—34.119 



—34.147 



Levelings of the axis were of course made as frequently as possible, and the 

 correction for inequality of the pivots thence deduced is — 0^013, the perforated 



