[ 476 ] 
iy6g 
April 
Ji—Z2 
2—26 
28 
Mean 
To find the Error of the Line of Collimation of the Quadrant. 
I letups board at the dlftance of about 300 yards, painted black, with two white marks on it; 
the diameter of each white mark = 3^ inches, and the diflance of their centers 1 j-£ inches = the 
difference of the height of the center of the telefcope, when the quadrant is inverted, and made the 
following obfervations. 
Zen. dill. of 
theupp.mark. 
Mean — 
Mean — 
89 50 00 
50 6 
4 
6 
o 
♦ 
o 
89 so 3 
Zen. did. of 
thelow.mark. 
oil 1 
90 
20 
20 
18 
*4 
16 
20 
20 
90 
7 
18,3 
80 
5 ° 
3 
179 
57 
21,3 
iSo 
O 
O 
2 
3 8 >7 
I 
19>3 
l The quadrant ia its proper pofitio*. 
, The quadrant inverted. 
To be added to the obferved zenith diflance. 
1 took the telelcope oft the quadrant, and adjufled the Uneot collimation lomething nearer. 
I found the error of the line of collimation of the quadt. in the fame manner, as on the 2ad, thus : 
Zen.difl.of the 
upper mark 
O / 
n 
89 51 
00 
S 1 
00 
51 
00 
51 
00 
5 ° 
5 6 
S 1 
4 
5 1 
6 
5 l 
6 
5 1 
0 
5 1 
6 
89 5 1 
2- 
Zen. dill, of 
the low.roark. 
Quadt. in- 
> its proper 
pofition. 
M«an — 
90 
// 
20 
12 
24 
20 
22 
20 
18 
16 
18 
20 
12 
90 
7 
18,4 
89 
5 » 
2— 
’79 
20,1 
1 80 
OO 
OO 
2 
39.9 
> Quadant inverted. 
To be added to the obferved zen. diflance. 
5 - 0 50 
A 7 .!?. This method is given us by the Rev. Mr. Nevil Mafkelyne, Aflronomer Royal, in hisdefeription 
of Mr. Bird’s aflronomical quadt. publifhed with his inflrudtions for the obfervation of the late Tran- 
fit of Venus, at the end of the Nautical Almanac of 1769, fee p. 23, and may be followed with great 
accuracy ; and to avoid the error that may fall on any two divifions of the quadt. as many different 
divifions may be taken as the obferver pleafts, by the fhifting the board that has the marks on it, 
higher or lower. 
