the Planet exterior to Uranus. 537 



Second. I trust that I am amply supported by the docu- 

 mentary history which I have produced in the view which I 

 first took, namely, that the discovery of this new planet is the 

 effect of a movement of the age. It is shown, not merely by 

 the circumstance that different mathematicians have simulta- 

 neously but independently been carrying on the same investi- 

 gations, and that different astronomers, acting without concert, 

 have at the same time been looking for the planet in the same 

 part of the heavens ; but also by the circumstance that the 

 minds of these philosophers, and of the persons about them, 

 had long been influenced by the knowledge of what had been 

 done by others, and of what had yet been left untried, and 

 that in all parts of the work the mathematician and the astro- 

 nomer were supported by the exhortations and the sympathy 

 of those whose opinions they valued most. I do not consider 

 this as detracting in the smallest degree from the merits of the 

 persons who have been actually engaged in these investigations. 

 Third. This history presents a remarkable instance of the 

 importance, in doubtful cases, of using any received theory as 

 far as it will go, even if that theory can claim no higher merit 

 than that of being plausible. If the mathematicians whose 

 labours I have described had not adopted Bode's law of di- 

 stances (a law for which no physical theory of the rudest kind 

 has ever been suggested), they would never have arrived at 

 the elements of the orbit. At the same time, this assumption 

 of the law is only an aid to calculation, and does not at all 

 compel the computer to confine himself perpetually to the con- 

 dition assigned by this law, as will have been remarked in the 

 ultimate change of mean distance made by both the mathe- 

 maticians, who have used Bode's law to give the first approxi- 

 mation to mean distance. 



Fourth. The history of this discovery shows that, in certain 

 cases, it is advantageous for the progress of science that the 

 publication of theories, when so far matured as to leave no 

 doubt of their general accuracy, should not be delayed till they 

 are worked to the highest imaginable perfection. It appears 

 to be quite within probability, thata publication of the elements 

 obtained in October 1845 might have led to the discovery of 

 the planet in November 1845. 



I have now only to request the indulgence of my hearers 

 for the apparently egotistical character of the account which I 

 have here given; a character which it is extremely difficult to 

 remove from a history that is almost strictly confined to trans- 

 actions with which I have myself been concerned. 



Phil. Mag. S. 3. No. 197. Suppl. Vol. 29. 2 O 



