370 
errors are very different in these cases; the first being at this 
Observatory to the second as 4 to 5; and I even think the 
stars ought not to differ in magnitude or colour: but if these 
precautions be attended to, I am satisfied that very exact con- 
clusions may be attained. Perhaps no stronger evidence of 
this can be given than the result of a second examination, in- 
stituted several years after certain alterations had been made 
in consequence of the first one. 
‘* As the value of y was not very much less than the whole 
that I had obtained with the former eye-piece, notwithstand- 
ing its low power, a new one was obtained from the late Mr. 
Dollond, of 240, and very good. Nine lines were inserted by 
Mr. Grubb, finer and more uniform than the previous seven ; 
the clock, whose are of repose had been four times that of 
escape, had its weight changed from 4 lbs. to 1:75; and amul- 
titude of trees and shrubs were removed from the south of the 
transit-room, as their evaporation was a manifest cause of un- 
steadiness. All these, except the alteration of the clock, 
tended to lessen the error; that improved the rate, but it 
made the beat less audible in high winds, and therefore would 
increase u. ; 
“¢ In this instance stars all of the first magnitude were se- 
lected ; one of them, Fomalhout, I had formerly been unable 
to use on account of its excessive fluctuations. They were 
a Lyra, 8 = + 38°. 39’. . . No. wires, 279 
a Aquile, $) BBG a ee 
Fomalhout, Ss SO Beadle, 23 ss Dee 
Giving 
(0° 1022)? = u? + y® x 163955 + 2? x 1°76909 
(00925)? = u2 + y? x 1°02225 + 2? x 210826 
(01162)? = u? + y? x 1:34559 + 2? x 163°81153 
Whence 
u=+0°0732; y=+050554; z= + 0°0049. 
