GEORGIUM SIDUS. 



Trom thefe data, M. de la Lande calculated the elements 

 of a circular orbit ; but it having been found that the 

 motion did not agree with any poflible circle, it became 

 ncceflary to calculate the elements of an elliptic orbit. 

 When a fufficient number of oppofitions had been obferved 

 for this purpofe, profefior Robifon of Edinburgh undertook 

 this invelligation, a full accoimt of wliich is given in 

 Edinb. Tranf. vol. i. 1788. The obfer\'ations on which 

 this invelligation is founded are as follows : 



■ {■ 0.046683 

 '{■ —0.000026228 



From which the following elements were obtained : 

 Mean dilbance - . . . 19.08247 



Eccentricity ----- 0.9006 



.Periodic time ----- 83.359 years 

 Mean anomaly at the Jth oppofition 4' 0^32' 51" 

 Long, of aphelion! forepoch Dec. J II 23 9 51 

 Long, of tlie node j 31, 1783. | 2 12 46 14 

 Inclination of die orbit - - O 46 25 



Equation of the centre - - 5 26 56 6 



The elements, as given by La Place, are as follows : 



Yrais. Days. Hours. Min. Scfon !s. 

 Sidereal revol. - - 84 29 o o 0.0 

 Semi maj. axis or mean diftance - 19.183620 



Proportion of eccentricity of feini maj. ^ 



axis for beginning of 1750 - 

 Secular variation ( — indicates diminu- 

 tion) ..... 



Dcg. Min. Sec. 



Mean longitude at beginning of 1750 - 228 33 53.6 



Long, of perihelion 1750 - - 166 36 48.8 



Sidereal and fecular motion of perihe-l ^ 



I- ^ }• o 4. 6.1 



lion . - - - - J"t- 



Inclination of orbit to ecliptic 1 750 - o 46 26.O 



Secular variation of inclination of orbit 1 



V • }■ O O ^.O 



to true ecliptic " " " J 



Loner, of afcendin;j node on ecliptic 7 a 



'=• ° '^ f 72 ^7 ?2.8 



1750 J/ 0/0 



Sidereal and fecular motion of node on 7 ^ 



r .• f O 57 16.2 



true ecliptic - - - - J -" 



The diameter of this planet is about 4I times that of the 

 earth, or ^5,1 12 Englifh miles nearly. When feen from the 

 earth, its apparent diameter, or the angle which it fub- 

 tends at the eye, is 3". 5, and its mean diameter, as feen from 

 the fun, is 4". As the diftance of the Georgian from the 

 fun is twice as great as that of Saturn, it can fcarcely be 

 diftinguilhed bv the naked eve. When the fky however is 

 ferene, it appears like a fi.xed liar of the fixth magnitude with 

 a blueilh white light, and a brilliancy between that of Venus 

 aid the Moon ; but with a power of 200 or 300, its difc is 

 vifible and well defined. Its arc of retrogradation is 3^ 36', 

 and the duration of its retrograde motion 151 days. 



This planet is accompanied by fix fatellites, all of them 

 difcovered likewlfe by Dr. Hertchel. The two firft, which 

 he faw for the firft time in the month of Jan 1787, proved 

 afterwards to b? the fecond and fourth, the others were dif- 

 covered fomc few years later. 



The 1110ft remarkable circumftance attending thcfe fatel- 

 lites is, that they move in a retrograde direftion, and revolve 



in orbits nearly perpendicular to the ecliptic, contrary to tlie 

 analogy of the other fatcUites, which phenomenon i.^ extreme- 

 ly dilcouraging when we attempt to form any iiypothefes 

 relative to the original caufc of the planetary motions. 



According to La Place, if we take for unity the femidia- 

 meterof the planet, equal to t".9, fuppofed feeii at t);e mean 

 diftance of the planet from the fun, the diftance of its fatcl- 

 lites will be as follows : 



I. 13.120 



II. 17.022 



III. 19-845 



IV. 22.752 



V. 45.507 



VI. . 91.C08 



And the duration of their fidereal revolutions 



D. Days. hrs. min. fee. 



La Place conceives that the firft five fatellites of the Gcor. 

 gian may be retained in their orbits by the aftion of its 

 equator, and the fixth by the aftion of the interior fatellites ; 

 hence he concludes that the pLinet revolves scout an axis 

 very little inchned to the ecliptic, and that the time of its 

 diurnal rotation cannot be much lefs than that of Jupiter 

 and Saturn. 



U/e of the Tails. — The general conftruftion of this 

 kind of tables will be explained under Pl.\net. The man- 

 ner of calculating the mean longitude of the planet u as fol- 

 lows. Vjnce's Ailronoiny, vol. iii. 



From Table I. take out the mean longitude, the aphelion, 

 and node, together with the arguments II., III., IV, V, 

 VI., VII., VIII., and place them in an horizontal line. 

 But if the given year be not found in that table, take the 

 neareft year preceding the given year as an epoch, and talce 

 out as before. 



Under wliich, from Table II. place the mean motion in 

 longitude of the aphelion and node, with the arguments pn- 

 fwering to the number of years elapfed fince the epoch, to 

 the given year. 



Under thefe write down (Table III.) the mean motions 

 of the fame, for the given month. 



Under thefe write down (Table IV.) the mean \jiptionsof 

 the fame, for the given day of the month. 



Under thefe write down (Table V.) the mean motions of 

 the fame, for hours and minutes. 



Add together the numbers in the feveral columns, rejeifl- 

 ing twelve figns, or any multiples thereof, if they occur ; 

 and in the arguments, rejedling 10,000 in the arguments IV., 

 VI., and looo in the arguments II., III., V., VII., VIII., 

 or any multiples thereof, and you get the mean longitude, 

 the aphelion, and node, and the arguments for the given 

 time. 



From the mean longitude of the Georgian fubtraiil tlie 

 longitude of the aphelion, and you have argument I., or 

 mean anomaly. 



With argument I. take out the equation of the orbit in 

 Table VI., together with the fecular v.iriation, with their 

 proper figns, except the time be Liforc 1780, in which cafe 

 the lecular variation is to be taken out witli a contrary fign, 

 making a proportion for the minutes and feconds of the ar- 

 gument, and you firft get the equation ; and doing the fame 

 for the fecular variation, you get the fecular variation ; then 

 fay, 100 : the number of years from 1 7S0 to the given time 



S 2 :: fecii- 



