Sun’s observed and computed right ascensions , &c. 441 
and extent of the exposure, to which the instrument was 
subjected. 
Table IX. indicates the portions of time, in which the pole 
star passed to the several wires, when the instrument was 
exposed to the sun’s rays ; whilst Table X. gives the like 
information, when the instrument was entirely defended from 
them. 
Table XI. shows the difference between the intervals of 
time, in which the pole star passed to the several wires, when 
the instrument was exposed to, and defended from, the sun’s 
rays ; and the results for two adjoining wires, are as follow : 
Seconds. 
— 0.17- 
— 1.25 
— 1.00 
+ 0.17 
+ 1-25 
> 
From the observations of 
1821. 
— 1.00 
— 0.87^ 
+ °-571 
— 0.33 
+ 0.50 ' 
+ 0.50 
From the observations of 
1823. 
Mean = — 0.15 
Thus it seems, that the time taken by the pole star to pass 
over any two adjoining wires of the instrument, is less when 
the instrument is exposed to the sun’s rays, than when it is 
defended from them, by 0.15 of a second; which, when 
quadrupled, and referred to the sun’s mean polar distance, 
is less than two hundredths of a second of time. 
