Sun's observed and computed right ascensions , &c. 433 
observer to direct the instrument to the reflected image of a 
star, a divided circle two feet in diameter, is attached to one 
end of the axis ; the pivots, originally of hard bell metal, 
having suffered an alteration of figure from constant use, were 
removed during the spring of last year by Mr. Troughton, 
and others, made of hardened steel, inserted in their stead. 
There is no apparatus whereby the observer, whilst making 
sidereal observations, can communicate to the instrument, 
azimuthal motion. 
With these exceptions, the Greenwich Transit is the same 
as mine ; the description therefore given of the one, will 
convey nearly an accurate idea of the nature of the other. 
The computed Right Ascension of the Sun, with which his 
Right Ascension as determined by observation, will be com- 
pared in the subsequent pages, is that given in the Nautical 
Almanac and Astronomical Ephemeris for the respective 
years, where it stands computed for the meridian of Green- 
wich ; the comparisons, however, being those arising from 
observations made at another station, viz. Blackman-street 
Observatory, it becomes necessary to inquire, how far equa- 
tions can be found, adequate to reduce the sun's right ascen- 
sion computed for Greenwich, to his right ascension when on 
the meridian of Blackman-street. This is a matter which 
observation must decide. 
Tables I. and II. show various right ascensions of the sun 
observed in Blackman-street during the years 1821 and 
1822; the former presents sixteen, the latter nineteen transits 
of the sun made on consecutive days ; the maximum differ- 
ence between the observed daily motion in right ascension 
