DIAMETER. 
to quit the difc, the diameter of Venus may be known-to a 
quarter of a fecon 
When the fecond limb of the planet touches the exterior 
femi- phar 
on the contrary, in the interior contact, Vcous is at D, a 
the diftance a ea centres is equal to the ai sciee of 
their femi-diam 
The fhorteft “diftance C Bis fuppofed known ; therefore, 
i D,CBE 
D, BF: 
f time the planet 
ela 
L 
" Bieard meafured the diameter of Mars on oe Sth Se ept. 
1762, aud it appeared to him to be 39”. ‘This obfervation 
redu cea to the mean diftance of the fun from the earth, is 
equal 11."4; by Rochon, 
according to Monnier, 9."9 3 
with a prifmatic micrometer, 8.9. 
The diameter of -Mars was very acurately determined by 
Dr. Herfchel, in 1783 (Philof. ‘Pranf. fi 
mates- a aaa $.”94, and the is fference of - = 
This aaa the 
from the 
ut nana prefer adire& meafure by a micrometer. 
The equatorial diameter of Jupiter is founs to exceed the 
polar diameter, in the proportion of 1.07 
The diameter of Saturn, ys by Pound, was 18", 
and ne Sua snkee of a ring 4 
Dr. Herfchel ot a cual many meafures of the 
laryer ring, makes it 46". e at the mean diffance of Saturn. 
‘Phe dimenfions of the two rings are in the following pro- 
porticnss 
Parts. 
1. Intide enna > the {maller ring - = 590 
2. Outfide dia - - 7510 
3. Infide diameter of the large ring - - 7740 
4. Outfide diam - - 8300 
5. Breadth of the i inner ring - - 80 
6. Breadth of the outer ring = 280 
4. Breadth of the fpace between the § rin - 115 
which may be thus expreffed in Englifh files: 
I. 146,345 
2 ————— 1845393 
Ze ————_190,248 
46 ——— 204,883 
5. = ~—-20,000 
6. ——— 7,200 
7 2583 
The diameter of the planet, at its mean diftence, is 1.8” 
on n exitts, relative to the ap- 
n 
ters {ubtend an angle of half a f{econd, at the diftance of 
the earth from the fun, but Mr. Schroeter eftimates Ceres 
at 3” 5, and Pallas 4”.5. 
The diameters of Jupiter’s fatellites have been eftimated 
by the time they employ to enter the fhadow of the planet. 
According to Bailiy, they fubtend the following angles, 
as feen from “Jupiter. 
L — 60’ 20% 
Il. —~—2z9 42 
II] —22 28 
I 
V. 9 39 
Mr. Schroeter, who has made a great number of obferva- 
tions on the fatellites of Jupiter, with a view 
faplay ing t e dine which the “fa llites take to difappear 
behind the body of ero ee 
they pafs ov This meth 
aoe hee | ca 
| I. Il. | {it , LV. 
Time es to enter 
the difk 235'1245/".3 | 544.5) 505 
Diameters es fom fis - = 
piter 3 O17! 13/418! SoM 7.32” 
True diameters in miles. 
15 toadegree - 594 | 455 818 | 570 
{n miles 60 to a degre 2256 | 1860 | 3272 | 2280 
In aie aii le of 
diam. of -| ae FE E 35 
Diameter viewed fon 
the ea YE perigee | 1.493] 1615 | 2.04 | 1.42 
The fame hel direct mea- 
furem 39 | r.09 | 2.27 | re4t 
By dine nai of the 
1.01 } Og: | 1.88 | —— 
Diam. a fie mean ae 
of earth from ©, that L ; 
of Jupiter being 3/13”.5 | 5.53 | 454 | 8.05 | 5.60 
Diameters. Jupiter be- 
ingfuppofedr - 0.0288) 0.0238! 0.0418} 0 0291 
Tbey do not appear to differ much in magnitude from 
each other, they are about ,1,th of the corti an or 
neatly one half of the diameter of the e 
Diameters of wa un, moon, and is tanets, according t to 
different aflronomer 
ren of the Sun. 
|Ariftarchus and = : = 
Archimedes |A.C. 260/30 0.0 |30 0.0 |30 0.0 
Ptolemy A.D, 120/33 20.0 |32 48.0 [31 20.0 
Albatenni 9OC/33 40.0 [32 280 131 20.0 
egtomontanus T46c|Z4 -O9 132 27.0 [31 Os 
‘Copernicu I5I5|33 §40 [32 44.0 '31 40.0 
yon TG7Ol32- 0:0 181 0.0 [30 -C.0 
Kepler IG00/31 4.0 130 3c.0 130 oo 
Riccioli 1640/32 8.0 }31 40.0 |31 0.9 
Jean Dominique 
Caffini 1666/32 46.0 |32 13.9 131 40.0 
Gaflcoigne 1640/32 50.0 ZL 40.0 
Picard and Au- 
\ 167 31 38 
Flamttead 1680}32 48.0 »f 30.0 
Mouton 1665/32 32.0 30 29.0 
De la Hire 1685|32 44.0 |32 11.0631 38.0 
Louville 172C)/32 37-7 131 32.52 
Jean Jaques Caf- ; 3 
fini I7ACI32 37-5032 5-0 131 32.50 
Hailey 1720 31 38 
Monnier a2. 504 
Bradley 
