0 
On the general Principles 
[J\N. 
equal accuracy with that which by any other instrument would consume the whole 
night, or perhaps more than one. I think, therefore, I am warranted in fixing l^or 
5'' 13 as the utmost error which latitudes, determined by it, need be subject to. 
This is equal to one-tliirteenth or one-tenth of a mile. 
21. Were the longitude determinable with equal correctness, there would he 
little doubt as to the superiority of the astronomical method for laying down a 
large tract of country, where no minute accuracy is required for special purposes. 
But this is not the case. Even with this admission, however, the facilities of this 
method are so great, and the advantage of its leading principle is so obvious, as to 
make it always a question of circumstances which method we are to employ ; 
and to afford some grounds for judgment, I shall go into a little detail on the sub- 
ject, and explain as succinctly as I can, the several methods of determining the 
longitude. n 
- 2 - . T1,e >; are in number seven. 1. The moon’s eclipses. 2. Immersions and 
emersions of Jupiter’s satellites. 3. The sun’s eclipses. 4. Occultaticns of the fixed 
stars.^5. The moon’s transits. 6. The moon’s distance from the sun or fixed stars. 
And 7, what is commonly called, The transference of time; whether effected by 
transporting chronometers, rapidly from place to place, or by signals visible at the 
same tune at the two stations of observation. ' e 
23. The first is not susceptible of much accuracy, on account of the ill defined 
edge of the earth s shadow, rendering it uncertain when the eclipse begins or ends 
11, s objection it is attempted to obviate, by observing and recording the entrances 
and exits of the several spots on the moon’s face into the shadow, and i nhtleS 
11, e mean of many observations of the spots will he nearer the truth than tl e mere 
commencement and end ol the eclipse. But it is, after all, far from giving ’"tlsfactor v 
results, add to which (a vital objection in our view of the subject) these phenomena 
occur so seldom as to be totally inapplicable to the business of map^/n ^nSr 
2 e c ]l pses of Jupiter s satellites occur oftener, and are susceptible of'» 
considerably higher degree of accuracy. Nevertheless, they fall short of a 
pose, and are better fitted to determine verv distant rtrwii \ ' , oU . ot . olu l nir " 
disposal, than contiguous poinS at Taeb o? ?. ',T .‘""V '* #t OUr 
several results of immersions mid emersions of the 1st satellite is'ran'ible " f 
the longitude to a very tolerable degree of accuracy but to n S»jI P k g,vin §‘ 
would consume months even in the favorable climate* of India ^ * a Senes * 
Jo. the sun s eclipses, and occultations of the C f.,ve 
pie to either of the preceding, and only inferior in practice on r J^nt°of 
motion ot the moon, on- whose position they depend The the slow 
fixed star is instantaneous, and if the commencement o/ I solHr^v ranC ? ° f a 
observable with such extreme accuracy, vet as observation ecll l )Se be not 
mg its continuance, the mean result may he expected to ll'"^ bt> n . mlti P lied dlu ’- 
curate than the solitary observation of the star. bS the mon *«' 
any uncertainty is greatly multiplied in the resulting LSI raol,on 18 ^ slow tin, t 
a second in the time of the phenomenon will occasion ^ ; an crro '' of *«» half 
whiih” S ‘ tUde -’ T 3 ! lf s P ace ; equivalent in India to three miles* IteV’ 1 " ho "‘ 12 *' in 
whether an interval co e..„.,.n __ . ^ . mee miles. 1 think it very doubtful 
1 st Deer. 
1st 
2 nd 
3rd 
4th 
5th 
6th 
7th 
8th 
9th 
10th 
31. 18. 
38,7 ^ 
35,5 ' 
«ach Ume 3 t ’l 1 resuf,""’ n!) ko " " l,ile 1 was vet quin- new to , lie 
undihc resui, ofeael, sot was^Seiv^u^'S *0 alllmt | 
24.— 
30.— 
31.0 
38,2 
34.7 
33.4 
37.0 
37.8 
32,6 
35.4 
Set 
do. 
do. 
do. 
do. 
do. 
do. 
do. 
do. 
do. 
^.Greatest difference from the 
■ mean 4 ", 4 . 1 
Extreme difference 7", 7 
Mean of 10 sets, or 100 obs. 
31. 18. 
35,4 
