14 



DIFFERENTIAL MEASTTRES. 



No. of niffhtsi 

 observed. 



Observatory. 



Instrument. 



Observer. 



Star of Compai 



rison. 



10 



Berlin, 



Great equatorial, 



Encke & Galle, 



b of Encke. 





6 



Cambridge, E. 



" 



Challis, 



7648 



B. A. 



c. 



7 



Washington, 



li 



Maury, 



7648 



& b. 





11 



« 



i( 



Walker, 



7648 



& b. 





4 



t( 



cc 



Hubbard, 



7648 & b. 





The place of the star a, viz., 7648 B. A. C, rested upon the following 

 authorities : Piazzi, Mayer, Taylor, Challis, 6 obs. ; Plantamour, 4 obs. ; Plana, 

 1 obs. ; Washington Observatory, 25 meridian observations. The above are 

 direct observations of 7648 B. A. C. There were also 5 Berlin and 3 

 Washington equatorial comparisons of 7648 B. A. C. with Neptune directly, 

 or through *6, on nights when that planet was observed on the meridian, and 

 its place reduced to a common date. 



The other star 6, (Encke's *«,) 9th mag., has for its place the following 

 authorities : Bessel's Zones, Encke &- Galle, 2 nights' comparisons with 7648 

 B. A. C. ; Encke, 5 nights' comparisons with Neptune, referred on those nights 

 to 15 meridian observations; Maury 6, Walker 10, nights' comparisons with 

 7648 B. A. C. 



The mean places of the two stars from all these authorities for January 1, 

 1847, were adopted, as follows : 



a = *7648 B. A. C. 7th mag., R. A. 1847, 327 32 16.79, Dec, 1847 — 13 23 39.17 

 J = star oof Encke, 9th mag., " 827 57 42.81, '' —13 25 57.22 



In this manner I obtained, from the above list of observations of Neptune, 

 16 normal places, which are subjoined, together with the corrections of the 

 Ephemeris. In this list, a and « are the mean places of Neptune as a fixed 

 star in geocentric longitudes and latitudes, referred to the mean equinox and 

 mean obliquity of January 1, 1847, corrected for planetary parallax, but not for 

 planetary aberration. 



• In my letter of February 13, 1847, to Dr. R. M. Patterson, Vice President of the Am. Phil. Soc, I stated that I did 

 not think that the error of either of these starsi' places much exceeded one second of space. Subsequent events have 

 strengthened this conclusion. — Author. 



