132 UNDISCOVERED PLAxNETS. 



of discovery but that of thorough telescopic exploration, which would, 

 indeed, be almost a hopeless task, were it necessary to examine minute- 

 ly every part of the Zodiac. But as these planets perform their revolu- 

 tions in a little more than four years, it is obvious that by making regu- 

 lar and particular observations in two opposite points, any moving bo- 

 dy discoverable by the telescope employed, must necessarily be detect- 

 ed in one half of that time. For half a century to come, this space 

 between Mars and Jupiter will perhaps afford greater probabilities of 

 successful examination than any other.* 



In the immense intervals between the orbits of Jupiter and Saturn, 

 Saturn and Uranus, and Uranus and Le Verrier, it is possible that simi- 

 lar bodies may circulate, at least equal in number to all the planets, pri- 

 mary and secondary, now known ; but at these great distances bodies so 

 small could scarcely be rendered visible by any instrument yet con- 

 structed. 



3. Whether there be any planets beyond the orbit of Le Verrier. The 

 distance of the nearest fixed star, Mj^ha Centauri, is more than two 

 Iiundrcd and ten thousand times the radius of the earth's orbit, or seven 

 thousand times the distance of Le Verrier's planet.f It would certain- 

 ly be presumptuous to aflirm that this vast interval is a cheerless blank. 

 On the contrary, the existence of planets more remote than Le Verrier, 

 may, we think, be regarded not only as possible, but as highly probable; 

 and if their magnitudes be equal to those of Uranus and the new pla- 

 net, undoubtedly one, if not more, may be descried by our telescopes. 

 Of this, however, there is not much probability for at least half a cen- 

 tury to come ; for, as the illustrious astronomer who developed the pla- 

 net which now bears his name, justly asks : "Who is tliere, who would 

 resolve to search for a telescopic star in the twelve signs of the Zodiac ?" 

 ])ut if, in the course of fifty or a hundred years, astronomers should de- 

 tect, in regard to the new planet, any want of agreement between theo- 

 ry and observation, the mathematician will again be enabled to calculate 

 the longitude of the disturbing body ; and, it is evident that when we 

 .shall have reached the limit of optical discovery, the orbit of at least 

 one more exterior planet, if any exist, may be accurately determined. 



* This is allogetlier improbable. The asteroids between Mars and Jupiter col- 

 lectively occupy the place of a planet, otherwise wanting in the series. — Ed. 



t The Linniean Journal of December, 1846, contained some estimates of the 

 distance, period, magnitude, Stc, of the new planet. These calculations were ba- 

 sed upon the assumption that its true distance was that indicated by the law of 

 Bode. The observations, however, which have been made, although necessarily 

 insutticietit i'or determining with accuracy the elements oC its orbit, render it pro- 

 bable that its mean distance is no more than about thirty times that of the earth, 

 or, 2,8jO,000,000 miles. The coirespoading peuod is about !().> years. 



