98 ASTR.EA. 



Ceres, Pallas, Juno and Vesta have been heretofore the only known 

 members. 



By the distance from the Sim and her periodic lime, she seems as 

 intimately connected with Juno, as Ceres and Pallas are with each oth- 

 er. Their periods differing but 28 days, and their distances 0.03, as the 

 eccentricities of their orbits are considerable and very nearly equal, 

 wliile their perihelions lie in opposite regions of the heavens, it follows 

 that their orbits cross each other in nearly opposite points, to wit : in 

 Leo and Aquarius. 



The intersection of orbits is not, however, peculiar to these two 

 planets, but is common to all tlie members of this family, each of which, 

 in its annual revolution, crosses the orbit of one or more of the rest; and 

 here 1 cannot help noticing an error, which has crept into that very in- 

 teresting and popular work. Dr. Dick's Celestial Scenery. 



The exceptionable passage is as follows : 



"Juno is further from the Sun in her aphelion, than Ceres in the 

 same point of her orbit; and Vesta is further from the sun in her aphe- 

 lion, than either Juno, Ceres or Pallas, at their perihelions. The peri- 

 helion distance of Vesta is greater than that of Juno or Pallas. Hence 

 Vesta may sometimes be at a greater distance from the sun, than either 

 of the other three, though her mean distance is less than that of either, 

 l)y millions of miles, so that the orbit of Vesta crosses the orbits of all 

 the other three; therefore, it is a possible circumstance, that a collision 

 may take place between Vesta and either of the other three, should they 

 happen to meet at the intersection of their orbits." 



The facts stated by Dr. Dick are correct, but the inference in res- 

 pect to the intersection of orbits is only true in the cases of Juno and 

 Pallas. But because the greater axis of Vesta's orbit lies nearly at right 

 angles with that of Ceres, it will not do to compare her apl»elion dis- 

 tance with the perihelion distance of Ceres, the true comparison lying 

 between the aphelion distance of Vesta and the mean distance of Ceres, 

 the latter of which distances is considerably the greater; and lience, 

 though the two orbits approach very nearly in long. 90° to 100°, they 

 do not cross; but that of Vesta remains within that of Ceres through- 

 out tlieir entire revolutions. 



This is the only exception to the fact, that the orbit of each of these 

 new planets crosses the orbits of all the rest. The inteiscctions of 

 Astra;a and Juno have been noticed, that of Astra^a and Pallas likewise 

 take place in nearly opposite points in sign 6 and 12. 



Astmea likewise crosses the orbit of Ceres in aboutlong. 5° and 115°, 

 and lliough her mean distance from the sun is greater llian Vesta's by 



