434 Mr. South on the discordances between the 
and the computed daily motion in right ascension, is 26 hun- 
dredths of a second in the one, and 22 hundredths in the 
other ; in the former table the mean difference of sixteen 
comparisons is only 4 hundredths of a second in time, whilst 
in the other it is only 3 hundredths. Hence, there can be no 
doubt, that we may safely enough employ the computed daily 
motion in right ascension, to arrive at accurate corrections of 
the sun’s computed right ascension, for the differences of 
longitude of the two observatories. 
Tables III. and IV. contain the sun’s right ascension com- 
puted for the meridian of Blackman-street, on such days as 
the sun’s transit was observed there, during 1821 and 1822, 
also the equations employed for the purpose ; the longitude 
of Blackman-street Observatory being 21.76 seconds of time 
west of the Royal Observatory at Greenwich. 
Tables V. and VI. exhibit the difference between the sun’s 
observed and computed right ascensions, as determined in 
Blackman-street during the years 1821 and 1822; these 
require explanation. 
The Observatory being situated in one of the principal 
manufacturing, as well as in one of the most populous, dis- 
tricts of the metropolis, the instruments were exposed to the 
inconveniences of soot falling upon them, from the chimneys 
of the neighbouring houses, steam engines, &c. ; and the 
transit, from the nature of the opening in the roof, came in 
for its full share: to protect its tubes, therefore, from the 
ravages of the soot, they were, shortly after the erection of 
the instrument, covered with green woollen cloth, which being 
neatly fitted and attached by buttons, afforded no incumbrance 
during the observations. The openings in the roof to the 
