Cll NOTES. 



sation with Sir John Herschel, during his visit to Collingwood. " You wish 

 for tidings respecting the planet beyond Uranus. I might refer you to friends 

 at Konigsberg who, from a misunderstanding, think they know more about 

 it than I do myself. I had chosen for a public lecture (on the 28th of Feb. 

 1840), the subject of the connection between astronomical observations and 

 astronomy. The public knows of no difference between the two, and it was 

 desirable to give them juster views in this respect. In shewing the develop- 

 ment of astronomical knowledge from observations, I was naturally led to 

 remark that we cannot yet by any means assert that our theory explains all 

 the motions of the planets. Uranus was adduced in proof of this, as the 

 old observations of that planet do not suit at all with the elements which 

 can be inferred from the later observations made from 1783 to 1820. I 

 think I once before told you that I had worked much at this question, but 

 that I had not arrived at more than the certainty that the existing theory, or 

 rather its application to the solar system, so far as it is known to us, does not 

 suffice to solve the enigma presented by Uranus. I do not, however, believe 

 that we ought on this account to regard it as not susceptible of solution. 

 "We must first know accurately and completely all that has been observed re- 

 specting Uranus. I have got one of my young auditors, Fleming, to reduce 

 and compare all the observations, and thus I now have all the existing data 

 before me. If the old observations do not suit well with the theory, the 

 later ones do so still less ; for the error is again already a full minute, and it 

 increases annually by seven or eight seconds, so that it will soon be conside- 

 rably larger. I have thence thought that a time would come in which the 

 solution of the enigma might perhaps be found in a new planet, whose ele- 

 ments might be recognised from its effects on Uranus, and confirmed by those 

 on Saturn. I was far from saying that this time had actually arrived, but I 

 mean now to try how far the existing facts may lead. This is a work which 

 I have had by me so many years, and 1 have already pursued so many different 

 views for its sake, that its completion has peculiar attractions for me, and I 

 shall, therefore, omit nothing to bring it about as soon as possible. I have 

 great confidence in Fleming, who at Dantzig, whither he is now called, will 

 prosecute for Jupiter and Saturn the same reduction of observations as that 

 which he has now performed for Uranus. It is, in my estimation, a fortunate 

 circumstance that he has, for the present, no means of making observations, 

 and that he is not engaged in any lectures. No doubt a time will arrive 

 for him also when he will have to make observations for a definite object; 

 and then he will, I trust, be as far from wanting the requisite means as he is 

 now from wanting the skill." 



