422 
Mr , Woodhouse's account of the 
Bradley's Observations. But no practical astronomer, I 
apprehend, can be so fond of encountering difficulties,* as to 
adopt this mode of adjusting his instrument; for, if from 
one set of equations he deduced the values of H, Z and C, he 
could not, by reason of his imperfect knowledge and manage- 
ment of the screws of his instrument, at once adjust it ; but 
would be again and again obliged to repeat his observations, 
and the solutions of the resulting equations. 
But this is not all. The differences of the clock's errors 
are the differences of the differences of the observed culmi- 
nations of stars, and their tabulated or computed right ascen- 
sions, and therefore must partake of the uncertainties to 
which the latter quantities are subject. The point to be 
aimed at in adjusting an instrument is, to adjust it by means 
that do not rest on the results of astronomical science. 
* As a kind of proof of the great uncertainty of determining the deviations of the 
instrument by the method of equations, I subjoin the following instance : 
October 13 , 1824 . 
Time by Clock. 
M 
Errors. 
h. m. s. 
s. 
s. 
a Aquarii 
21 56 52<86 
48.72 
4.14 
a Pegasi 
22 56 8.74 
4 -4 
4-34 
a Andromedse 
23 59 27 .7 
23.25 
4-45 
whence, the axis being horizontal, and the clock going sidereal time, we have these 
equations : 
— 1/^ -j- t — .8028 Z ^ C 
— 4.34 + £ = .6347 Z + 1.032 C 
— 4.45 + E == .4627 Z + 1.114 C 
from which, Z zz i'.48, C = ; but if an error of oVi had occurred in the ob- 
servations, or if we suppose the tables to be erroneous to that degree, and the 
second equation had been 
— 4*.44 + £ ■=: .6347 Z + 1.032 C, 
then, instead of the preceding values of Z and C, we should have had these : 
Z = 2«.935 
C = 6.033 
