DIAMETER. 
greater circles as 10000 to 31445; in which ie a 
tolemy, Vieta, and Huygens, agree with Van 
etius 8 us the 
‘mott accurate 
not erring” 33 : 
chimedes’s, Metius’s, or the pice of x to 3.1 
The Diameter of a circle given, t 0 find the aa 
erence and area; and the cirumfere being tape to Eh the 
diameter.—The ratio of the diameter to the circumference 
eing had, as in the laft article, ae of the a 
wife, 
cicumference will be 3r4, and the cle 
But the fquare of the nieces is 10000: therefore, this is 
to the area ‘es the circle as 10000 to o that is, a8 1000 
to 735 nearly 
The area of the circle being given, to find the DiaMirER.— 
o 785, 1000, ard the given area of bee circle 246176, 
find a fourth eo viz, 311360 h is the 
is of the diameret. Ont of this ea the fquare 
cot, ae ie is the Gon itfelf. 
ER of a conic fesion is a ‘ight line bifeCting all 
the eee &e,. c Seéfions. 
“is, when it cuts ae faid lines at right angles, is more 
particularly called the axis of the curve, or [ection 
IAMETER, Lraa/ver/e, isa right line, which ‘pat ing con- 
tinued each wi between two curves, bife&s paraliel right 
lines between the fare. 
Diamerer, ‘Con onjugate, is a right line, bifeGting lines 
drawn eld to the tranf{verfe diameter. See Coryu- 
GATE. 
AMETER of any Curve, is a right line which divides 
two other parallel right lines, fo that in each of them, all 
the fegments or ordinates on one fide, between the diameter 
and different points of the curve, are equal to each other. 
This is Newton’s fenfe of a 
iameter us to 
fome iamete hat line, whether right or curved, which 
bifeéts all the euuunaae drawn from one r of 
a cu 18 every curve will have a diameter ; 
and hence the curves 3 of the /ceond order, have, all of nip 
either a right-lined diameter, or elfe the curves of fome o 
of the conic {eGions for diameters. And many eooneeeeal 
curves of the higher orders may alfo have for diameters, 
curves a — ig ordcrs 
Diam a fphere, is ‘the diameter of the femicircle 
by whofe. pee the {phere is generated ; called alfo the 
axis . e {phere 
TER sR of gravity, is a right line pafliag through the 
a ‘in Aflronomy, is either apparent or real. 
‘The apparent diameter of a heavenly body, is the sat 
which it fubtends at the place of the obferver, and it varies 
inverfely as the : ftance, becaufe {mall angles are propor 
to their tangen 
yo Sree ietions of the apparent ST of the 
is we are enabled to afcertain their true diameters, 
itujes, having previoufly found ie diftance. 
CE 
AN 
In the triangle TAB, (Plate IX. Fee Sig. 64 ) 
which the angle B is aright angle, we have this aaa : 
:fo. ATB:: TA: "A 
thus the true diameter A B is ning by multiplying the 
diftance T A byt oe fine of the anzle A TB, which is the 
apparent aaa e planet. 
‘The apparent lates of the fun is ea! changing, 
and the law a its variation affords a {trong proof of the el- 
a natnre of the earth’s orb‘t, and cut the motion of the 
Xd. 
® 
earth i is really flower, as its diftance from the fun 1s ae 
or the diameter of the fun is about 31’ 31” in fummer, an 
32! 36” in winter; from which it 1s evident, that its difaree 
in fummoer is to its diftance in winter, 2s 32’ 30" to 31’ 31” 
ourly motion of the fun in winter 13 2’ 3373 an 
2° 96" 2 31" 31" 2 OP ; 2/28", There ic, the hourl 
i 2' 28", . it was rea a uniform, 
ee dilkanee (oni the fun. 
motion in fummer is only found to be 2’ 23” 
the diminution of 5” caufed by the increafe of diftance, there 
can 0 het be attributed 
toa cabin of veloci n of the earth. 
only ee se application o of Fleleopes ie iene 
ene ameters of the fun and pianets have 
be een ac cuvately Fone ae 
There are feveral methods of determining the wand 
of the fun: By micrometers; by obferving the time of i 
paflage ever the meridian wire of a tranfic inftrument ; ‘es 
the difference of altitude beraeen its upper and lower limb, 
cae hee 
as obferve el a mural le aan or good circular inftru- 
ment, or by a repeating ci 
T 
e meafuremeats hich Sane — been confidered as 
the beft, and which ¢ been adopted in our folar tables, 
have been made with eat micrometers. De la Lande, 
in the year 1760, pies the diameter (apogee) 3’ 305”. 
Dr. Mafkelyne 3 '26"2. ort, with an Anes glafs mi- 
peak app lied to a two foot telefcope, Ther 
siete fome {mall uncertainty in the Ee ae ‘by a mi- 
cr saree he difficulty of obtaining the accurate value 
of its fcale oe divifions. Some {mall difference will likewile 
rife from the nature of the telefcope employed. 
A good aftroromical circle, moving eafilyin azimuth, would 
be well adapted for this ceianle aa oy feveral obf-rva- 
after the meridian. paffage, 
and t a ane of altitude, appiied by the 
table | for that purpefe, and which we have given 
under Dect 
erhaps ie repeating circle of Borda would be ftill pre- 
ferable. Of the extreme accuracy that may be obtained by 
repeating the angle, even with a {mall inftrument, we may 
form fome idea from a feries of aifince des "Temp M. 
e 
ycar 1803. e rep 
fun a thoufand times, and fe erations divided inte ten 
parts of one hundred each, were as 
5° 32’ 30” Diameter (apogee). acai ees | 
a 3° 31 30 
52 33 31 318 
33 ———— 3r 318 
3f 31 30.6 
33 31 318 
29 31 29.4 
30 30 31 303 
34 30 31 32-7 
go Br go 
Mean 31! 31”. 
The ae ufed was a reficGing circle of Borda of 5 
inches radiu 
cane y is the fame as is adopted by Delambre in 
his folar tables la’ely publithed. au to this article is a 
table of the fun’s femidiameter to ev degree of mean 
maly. The variation in the a pact femidiameter of 
h the variation of the tun’s horizon- 
dcereafe torether, and inverfely as le diftance of the two 
48 . bodys 
