214 The Orbit and Motion, of 







to the obfervations of Dr MASKELYNE and Mr SLOP, made 

 with inftruments equal to any in Europe, this inaccuracy 

 fhould not be fuppofed greater than 5". With refpecl to my 

 own, I will allow it to amount to 10". 



THE queftion is now, upon what good principle we may 

 prefume to correct the obfervations. When the Planet appears 

 flationary, we have the beft opportunity of afcertaining its 

 diftance from the Sun, by means of an imperfect knowledge 

 of its angular motion, . the earth's diftance from the Sun afford- 

 ing a bafe moft advantageoufly fituated. Mr MINTO has com- 

 municated to me Mr SLOP'S obfervations of the Planet when in 

 this fituation. On 1782, March, 6 d. 6h. 14. 56". M. T. 

 Greenwich, the apparent longitude of the Planet was obferved 

 2 j. 28. 49'. 27". on the Ecliptic. The five obferved oppofi- 

 tions give us the firft and fecond differences of the heliocentric 

 motion at thofe oppofitions. By thefe means we obtain, by the 

 ufual methods of interpolation, the heliocentric place of the 

 Planet at the time of the above obfervation, and this without 

 an error amounting to 2". By comparing this with the geo- 

 centric place, we obtain the Planet's diftance from the Sun 

 =: 18,9053. By making a fimilar interpolation for March 7^. 

 (? b. 14'. 56", we obtain another heliocentric place of the Planet. 

 The difference of thefe two places gives the diurnal heliocen- 

 tric motion 43 ",4365. But a Planet defcribing round 

 the Sun a circle whofe radius is 18, 9053, will have its diurnal 

 motion = 43", 1647. 



FROM this it is demonftrable, that the Planet's diftance from 

 the Sun is greater than half the parameter of its orbit ; and 

 that its true anomaly, or diftance from its aphelion, is more 

 than 90 *. On the other hand, we find, from the continual ac- 

 celeration of its motion, that, at the oppofition 1785, the Planet 



had 



* FOR the angular velocity of a body in an ellipfe, is to that of a body in a circle, at 

 the fame diftance, in the fubduplicate ratio of the half parameter to the diftance* 



