GOULD — REDUCTION OF D'AGELET's OBSERVATIONS. 31 



The resultant differences Lalande — d'Agelet are — 



A a = — Os.029 by 820 stars ; A d = + 1".29 by 832 stars ; 



= — .031 by 1,341 observations; = + 1 .27 by 1,354 observations. 



There remain 206 stars, of which all but 16 have been identified as observed by other 

 astronomers, viz : 110 in Bessel's zones; 14 in Johnson's Radclifl'e catalogue; 10 in Argelander's 

 northern zones ; 2 in Argelander's southern zones; 10 in Rumker's catalogue ; 33 in Argelan- 

 der's D urchmusterung ; 7 in Lacaille only, and 4 in other places. The examination of the aver- 

 age differences between the positions of the present catalogue and those of the authorities above 

 named has only been extended to these few stars, but gives entirely satisfactory results. 



Thus the difference, Weisse's Bessel — d'Agelet appears to be — 



Between Oh. and 13A. ^ a = -\- 0s. 15 by 38 observations. A (5 = — 4". 19 by 37 observations. 



13 and 23 = 0.00 60 " =—1 .57 04 



JL-au of all = + .06 98 " = — 2.53 101 



The number of unrecognized stars amounted originally to 55; and in my uncertainty 

 regarding them, I applied to my friend Mr. Ferguson, Assistant Astronomer at the Washing- 

 ton Observatory, who in the kindest manner responded to my appeal, and together with Prof. 

 Asaph Hall, of the same institution, examined with the great equatorial of the observatory the 

 regions in which d'Agelet' s observations placed each of these 55 stars. The aid thus rendered 

 by these experienced observers has enabled me to make plausible assumptions for the greater 

 part of the cases, and has reduced the numbers of stars now missing or discordant, by an 

 amount not susceptible of explanation, to 16. A list of these will be given below, and notes 

 concerning 12 others will be found at the end of the catalogue. These 28 stars are indicated 

 by a dagger (t) against their respective numbers. 



§ 13. GENERAL REMARKS. 



Since the observations of d'Agelet are the earliest, excepting Bradley's, of all the obser- 

 vations belonging to the more accurate class, we may reasonably rely upon the proper-motions 

 deduced by comparing them with recent determinations. One of the earliest cases to attract 

 attention was the well known "Argelander's star," or 1830 Groombridge, whicb was observed 

 three times by d'Agelet, thus enabling us now to deduce a yet closer value for its proper- 

 motion.* There are in the present catalogue about 1400 well recognized stars, which do not 

 occur in the Fundamenta Astronomic?, but have been observed in recent years, and for the most 

 of these the proper-motions hence deduced promise to be more trustworthy than any others now 

 attainable, unless some large number of modern observations of high character permits the 

 application of the method of least squares. 



The differential character of the reduction does not militate with this view, inasmuch as 

 the places and proper-motions of the standard stars on which the determination rests may 

 apparently be relied on to a degree far within the mean error of a quadrant-observation in 

 1783. A gratifying indication of the general trustworthiness of the catalogue is afforded by 

 some of the dates already mentioned, on which the number of standard stars proved inadequate 



*Tbe most probable value which I have found is -f- 0s. 3430 in a. and — 5". 7923 in <! ; tin- mean place of the star for 

 1800.0 being 11*. 41m. 24s.20, -f- 39 9' lit". 47. 



(31) 



