Astronomy. 447 



great as the one I have given, as also a mass which may be but 0*63 of 

 the same. And in order to have a mass but half of that which I have 

 given, we need only to carry the uncertainty of the modern data to 

 7"*4. This therefore presents no difficulty. 



To recapitulate : 



I announced in 1846, that on a given day, might be found in a 

 given place, a planet that would account for the perturbations of 

 Uranus. And the astronomers of Berlin found on the day, and in 

 the place indicated, a planet which does account for the perturbations 

 of Uranus. 



This coincidence was not accidental. Suppose I were to-day, Oct. 

 2d, 1848, to make known to the Academy, for the first time, my* work, 

 and having deduced the place where we ought to look for the planet 

 this evening, we should immediately discover the body, at a distance 

 less than a degree and a half from the position we would have thus 

 assigned it. The prediction would have been equally exact in 1837 or 

 1827. At any epoch an observer would have found the planet within 

 the limits which my calculation assigned it ; and during 120 years these 

 limits have not exceeded those which I gave even in 1846 ; limits which 

 were printed before the discovery, in our Comptes Rendus, and after the 

 discovery of the body in the Connaissance des Temps. 



It results in short, from my theory of limits, the exposition of which 

 I have given on pages 239-249 of the memoir of 1846, that the ele- 

 ments of Neptune deduced from observation, do not differ from the 

 predicted elements more than the uncertainty of the data authorizes. 

 The proof is unanswerable. 



Among the periodical comets recently discovered, there is not per- 

 haps one, the theory of which, founded upon actual observations made 

 during one appearance, would give, after sixty years, the longitude 

 with as much certainty and precision as I have obtained. 



Allow me to speak with freedom. When I announced my principal 

 result in 1846, 1 found scarcely a person who would believe it. De- 

 duce the position of a planet from a little derangement which it caused 

 in Uranus! What folly! it was said. But those who spoke thus, are 

 precisely the ones, who, at the present day, find it altogether intoler- 

 able, that I have not succeeded in giving the position of Neptune for 

 e ighty years, without an error of more than 7£° at the end of this 

 period, and who think the world ought to make a severe example of 

 me. — Comptes Rendus Acad. Sci., Paris, October 2d, 1848. 



2. Indication of a Method of testing Older s^s Theory respecting the 

 common origin of the small Planets ; by S. Alexander, (from Nos. 

 658 and 659, of the Astronomische Nachrichten ; communicated for this 

 Journal by the author.) — Since the discovery of so many new planets 

 in the region between Mars and Jupiter, the hypothesis of Olbers with 

 respect to their origin has, of course, received renewed attention. 

 Any thing which may have a tendency to confirm or to refute that hy- 

 pothesis cannot fail to be of interest. I would therefore respectfully 

 propose a mode of investigation which, if successful, might afford a 

 plausible confirmation of the hypothesis of the explosion of a single 

 planet in the region in question, or else show, with an equal plausibility, 

 that no such event could have occurred. 





