[ 269 ] 
Adjuflments of the telefcope with the different eye-pieces and little fpcculunis, as.ccnihined 
together when ufed. N. B. — Ihews that (o) on the vernier, is behind, or to the left hand cf 
the firll divifion on the fcale ; and -f to the right hand, or before. 
Long eye-piece and (hort focus little fpeculum magnifying loo times rr: — o + 1 on vernier. 
Long eye-piece and long focus little fpeculum with micrometer on ~ — o -f 19J on vernier. 
The eye-piece with moveable wires, and long focus little ipccu- ] 
lum, and micrometer j — n- o 4 on vernier. 
Thefe are a mean of 10 or 12 obfervations each. 
The Value of the Scale of the Object Glafs Micrometer was found as follows : 
A bale of 120 feet was carefully meafared on level ice (which was covereef with frozen fnow 
about half an inch thick), with two 10 feet hr rodsj and the mcafure being taken four different 
times, no one differed from any of the others fo much as -j-Lth of an inch. But as the fir 
rods might not confift of 10 feet exadtiy of the fame ftandard from which the micrometer fcale 
was laid off, I therefore took fix inches betw'een the fine points of a pair of compaffes, from 
the micrometer fcale; and, by repeating this meafure, found the exadtlengch of the fir rods in 
raeafures of the micrometer fcale ; and thence corrected the length of the bafe, found imme- 
diately by the rods, and reduced to the llandard of the micrometer fcale. Perpendicularly 
over the bafe, at one end, was placed the center of the divided objedl glafs, and perpendicularly 
over the bafe, at the other end, a board was placed, having its plane at 
right angles with the bafe line, white paper palled on its upper part ; and 
at the height of the center of the objed glafs, nearly above the horizon, 
was a ftrong black line drawn, as A B rr 8 inches, A ^ and A ^ being fmall 
but equal diftances from A; by bringing {ed&nA gh) to coincide alter- 
nately with (A^) the error of adjuilment of the micrometer fcale was 
found ; and by feparating the glaffes till (A a) and (B h) made but one 
line ; from this feparation the value of one extent of the micrometer fcale was found, by mak- 
ing this proportion. As the length of the bafe : is to the length (AB) : : fo is 206265" (the 
number of feconds in an arch equal to the radius of a circle) to a fourth number, which will 
be the feconds of the angle meafured by that opening of the glaffes, which is Ihewn by the 
micrometer fcale ; and other angles will be in diredl proportion to the refpedlive meafures 
whence the table was formed. 
d h 
A 
ZENITH DISTANCES taken with an Aftronomical Quadrant, of one Foot 
Radius, made by Mr. Bird, at the NORTH CAPE of EUROPE. 
Bar. Ther. 
Inches. 
out 
in 
0 
0 
1769 
0 May 14 
29,80 
43 
40 
20 
29 ’ 7 I 
45 
41 
h June 3 
29»93 
66 
58 
1 1 
-9>S7 
46 
42 
15 
29,66 
41 
40 
16 
29,7c 
+4 
39 
‘7 
29,72 
44 
42 
29,71 
4 / 
48I 
29,70 
52 
S'i 
29,70 
52 
542 
29,18 
52 
O U. L. on the mcrid. 
O L. L. ditto 
O L. L. 
O u. L. 
G L. L. 
O U. L. 
O U.L. 
0 L. L. 
? Center 
O L. L. 
O U. L. 
Arflurus 
O L. L, j on the north 
O U. L. J meridian, 
a. Lyras 
§ Center 
Interior arch 
Exterior 
arch 
Exterior arch 
reduced 
d 
H 
o 
t) 
n 
H 59 
51 50 
48 52 
±2 20 
t 
+7 35 
47 54 
52 13 
47 50 
47 
50 36 
85 7 
32 25 
52 27 
10 
5'5 I z6 
40,0 
54 2 12 
44,0 
52 0 18 
54.0 
5129 
5 1 I 1 1 
37,0 
50 3 £ 
50 2 r 
27,8 
51 0 13 
36 + 
55 2 27 
28,0 
510 /> 
50,0 
50 I 28 
8,0 
53 3 3 <^ 
91 I 12 
2Q-f 
90 3 ( 
iS-k 
34 2 I! 
1 
51 
5 ‘ 
i6: 
o 
12 
c 
48 
48 
48 
47 
8 
'4 
47 
47 
T/ 
K 57 
i( 50 
zr 35 
^ ^5 
0,0 
2 ^ 
58 59,2 
io 45’9 
52 3656 
20 49,8 
7 26,7 
31 4°>3 
22 4(,3 
54 33.8 
13 2?’4 
50 So,S 
18 42,0 
36 21,2 
37 4'U 
7 
2 ^ .z. 2 J O 
26 55,4 
From 
