1801. ] 
of my very good friend, Mr. Charles 
Bouchar ; yet, I dare not promife to my- 
felf the like favour from you on any other 
grounds than that I am a true honourer 
of your warth, and a_ well-willer to 
aftronomy and all its followers. You 
may perhaps have expected that Mr, 
Bouchar fhould have returned you thanks 
‘for the great trouble he put you to by 
his re; he doubtlefs would have done it, 
had not his occafions called him, foon 
after the receipt of your’s, to take a 
voiage to Jamaica, where he will not neg- 
lect to make what obfervations he can, but 
elpecially thofe of Mercury, for which that 
horizon will be mof convenient. Since 
his departure, I have been wholly deftitute 
of acoadjutor in my fludies ; yet, when- 
foever the heavens favour us with fereni- 
ty, I omit not to make what obfervations 
I, may of the planets, being reafonably 
well provided with infruments in which I 
can confide to one minute without error, 
by means of the telefcopicall fights, and a 
fkrew for the fubdivifion ; by my quadrant, 
fo furnifhed, I haye obferved Jy and 2 
to differ confiderably from Hecker’s Ephe- 
meris, which makes fh at leaft 20’ in 
confequence to his vifible or true place, 
but 2 about 8’ in antecedens; nor doth 
S:reet’s Caroline Tables reprefent fh much 
better, for inthe Obfervations of Hevelius, 
Aug. 4% 1670, Philos. Trans. Num. 65. 
Pa. 2089, bh was feen 108 5° 15/25" 3 
zk ¥, with fouth lat. 1° 54’ 11", but 
by the Caroline Tables J was in 
10° 5°'ag 927, die 17) 7", im. the: fame 
lat. precifely: and, according to Hecker’s 
Ephemeris, he was in 4°? ir’ of } lat. 
auftr. 1° 53’ ;-19-+obler.—whence fo 
great differences fhould arife is hard to 
conjecture; however, future cbfervation 
will declare, whether it be the fault of his 
eccentricity oy middle motion: if you 
have obferved any thing of the like nature 
in Ip, I beg you would communicate it. 
Your obfervations of 2{, publifhed in 
Philos. Trans. Num, 82, make 2f 13! in 
confeq. to Hecker’s Ephem. and _ thofe 
Num. 87. diff. 8’, the fame way, agreeing 
with mine precilely ;—c 1 find little 
fault with; yet, about his oppofition to 
the fun, he was near upon 5’ in confeq. to 
Hecker’s place. If you are_pleafed to 
fend me any of thofe moft accurate obfer- 
vations ‘you do daily make, wiereby I 
may confirme mine, I thal) ever own it as 
a fignal obligation, and fhall endeavour to 
return my gratitude by making any ob/er- 
vation you fhall defireme. I requeft that 
you would fend me Caffini’s Suppofition 
of the Hight of the Atmofphere, and the 
S 
Original Leteers of Drs Halley: 
Horizontall Refraétion, and -what other 
hypothefig he hath of the Doctrine of Re- 
fraction, and whether experiment hath 
been made to confirm thofe quantities ; 
to me it feems to vary from any certain 
rule, and to be fubjeét to the accidents of 
the heat and cold, which may confiderably. 
alter the denfity and altitude of the {phear 
of air, and confequently alter the refrac- 
tions made in it, which feems to be con- 
firmed by comparing the refragtions of 
the funn with thofe of the fixt ftars ob- 
ferved by Tycho, where the flower decreafe 
of the funn’s refractions argues a greater 
hight of the atmofphere, as if the prefence 
of the funn did elevate the air, which if 
fo, the afternoon refraftions would be 
greater than the morning’s, and thefe un- 
certainties will make the place of & du~ 
bious to 2’ or 3/ in moft obfervations that 
can be made in our climate. 
The late eclipfe of the moon, Jan, 1, E 
obferved at London, with Mr. Street, as 
followeth :—The precife beginning we faw 
not, by reafon we had not fitted our in- 
ftrumznts foon enough, trufting too much 
to the calculation, but 2 of a digt. were 
eclipfed when the upper limb of the } was 
11° 39 high at- 55 3072; the immerfion 
was, when Pollux was high, 27° 15’ a 
6" 25™Z, emerfion at Pollux 41° 35%, 
9% 68m—The jut end, when the } lower 
limb was 42% 30! high, time g? om4, 
whence the middle may be 72 12m, We. 8! 
too focn for the calculation of Mr. Ste- 
venfon.. During the time of totall dark- 
nefs, the moon covered a ftarr of the 6 
mag. viz. 29 of It, the immerfion was 
15° or 16° from the nadir toward. the 
weft, when Pollux was 33? 5’ high, 
7h 37415 but the emerfion was 75° from 
the nadir toward the weft, ali. Pollux 
37° 45’—7> 42™ 20";—what you or your 
friends have obferved of this eclipfe, I 
entreat you to fend me.—One thing more 
I thought fit to fignifie to you, that is, 
thai the 13th and 20th of }€ are errone- 
oufly placed in Ticho’s Catalogue, the 
13th is there in 14° 19! of Y. 0° 57'4, 
lat. bor. but its diftance from Ala Pega 
is 16° 36° 30", and from Cinguli Andre~ 
meda28? 4! 15"; whence I computed his 
place in Y 14° 19'f, with fouth lat. 
o° 11! 50";——and the zoth is 1n 229 12/ op 
with 1° 38’ bor. lat. but by his diftance 
from Lucida ¥Y is 15° 45’ 5", and from 
Os Cetitg? 44'45" I computedits place in 
22? 11' 17" cum lat. aus. 1? 40’ go!;—~ 
moreover, I am fully fatisfied that cor 1 
is at lealt 5’ in antecedence t0 his Tiche- 
nic piace, which is confirmed by ‘Ticho’s 
own obfervations, who, sth Februari 
inane 
’ 
