12 
Description of a Repeating Circle. 
[Jan. 
intermediate interval, and consequently, if neglected, will occasion an error of 
about three minutes of longitude in the deduction. This circumstsnce is thus spe- 
cially adverted to, because its notice is omitted in the very useful summary of the 
minute corrections, requiring attention where precision is desired, published by 
the Secretary of the British Board of Longitude, in the Journal of the Royal Insti- 
tution, for July 1820. # 
The circle with which the distances were observed, was ten inches in diameter, 
and weighed five pounds ; the telescope was furnished with a magnifying power of 
fourteeu. The observations at Sierra Leone were not strictly its first employment, 
as I had observed sixty-four distances with it at Madeira, on the outward passage ; 
with the exception of these, however, the use of the circle was new to me at Sierra 
Leone, and the awkwardness which attends the employment of a new instrument 
Was still to be overcome. 
The sixty-four distances at Madeira, of which forty were of Regulus, west of the 
Moon, and twenty-four of the Sun, east of her, made the British Consul's house, at 
Funchal, in 16° 55'00' V/. ; the longitude ot the Consul’s garden has since been as- 
certained, by the mean of sixteen chronometers, specially sent for the purpose, at the 
direction of the Commissioners of Longitude, and has been found 16° 54'. 45',3, 
W. 
The preceding tabular statement 4 comprises the results of 1350 distances, divi- 
ded into 123 sets, and distributed through seven stations. The following table col- 
lects, in one view, the mean results, and exhibits a summary of the differences of the 
individual sets on the general mean at each station. 
X 
Individual Sets differing 
from 
the 
QJ 
CJ 
S3 
Mean. 
Stations. 
cd 
Q 
Ifj 
(A 
G 
jS i 
5 Cf. 
3 _a* 
£ GC 
5 
- a. 
1 i 
5 cc 
X ® 
- & 
Mean 
Longitudes. 
o 
o 
£ 
+- ••• 
/r r * 
i— > • <— • 
X *“ 
* E 
w •« 
75 
-*-> • — • 
£ 
6 
£ 
6 
5z; 
X 
-3 
-3 
£ 
*3 
s « 
-3 
/. co 
a* 
3 
Sierra Leone, 
318 
23 
4 
7 
4 
7 
0 
0 
l 
13 
15 
26,8 
W 
St. Thomas, ~ 
150 
11 
2 
4 
1 
2 
2 
0 
0 
6 
45 
00,4 
E 
Ascension, ^ 
164 
16 
5 
2 
2 
5 
2 
0 
0 
14 
23 
35, 
W 
Bahia, 
128 
14 
5 
4 
3 
2 
0 
0 
0 
38 
32 
39 
W 
Maranham, „ 
Trinidad, — „ 
158 
162 
16 
16 
12 
5 
3 
6 
1 
5 
0 
0 
0 
0 
0 
0 
0 
0 
44 
61 
21 
36 
25,5 
15 
W. 
w 
Jamaica,—.. 
270 
27 
15 
7 
4 
1 
0 
0 
0 
76 
53 
15, 
vv. 
rOttllj 
1350 
123 
48 
33 
20 
17 
4 
0 
1 
.7. oinma .1 circumstances ot Observation i o. 
on shore, and within the tropics, the observer being previously accu tmS’t i * 
observation with sextants, and furnished with a correct knowled ? to lunar 
station.-it is about 2 to 1, tlmt a sing^et^ at 
served with Mr. Dollond’s circle, will Jive a ^,uTwbl,?„ , u rt,s ? a " ces > ° b - 
tmle, deduced from an extensive seriesf including !°" gi ' 
phere occurring in such climates, and at different periods M . f . the atm ? s - 
it is about 2 to 3 that the result will be within nnp ;i i ,, l)on s > that 
amounting to so much as between 4 and 5 miles * difference » 
oftener than about once in 25 sets. ’ ^ not ex P ect ed to occur 
Ihe improvement which practice will ti,„i i •. , 
consequently on the inferences that liavebeen Lted^ ( and 
of the table ; for if the three last stations only are regarded the eh ° n 311 ,n * pectlon 
more than equal, that the result of a single set is within on c } Vdncc * Wl]1 appear 
only whU8t the “ 
MOSS’S 
tal^£ 8teme,ltS “ as the i. ~ clearly expressed in the above 
