XXX BIOGRAPHICAL NOTICE. 



He experiences also a difficulty, which all young writers feel more or less, in putting 

 into shape and order what he has done, and well done, so as to convey an adequate idea 

 of it to others by writing. After receiving your questions it occurred to him that it 

 would be well for him to send you a full account of his methods of calculation, and 

 that he might send the answer at the same time. I believe that nothing but procrasti- 

 nation in fulfilling this intention was the reason of his not sending an answer at all. I 

 have always found him more ready to communicate orally than by writing. It will hardly 

 be believed that before I began my observations 1 had seen nothing of his in writing 

 respecting the new planet, except the elements which he gave me in September written 

 on a small piece of paper without date. 



" I first got an idea of the nature and value of his researches by an abstract which 

 he drew up to produce at the meeting of the British Association at Southampton. The 

 public would hardly take such a reason as that I have mentioned to be the true reason 

 for his not answering your question, and I fear therefore a hiatus must remain in the 

 history." 



As the Astronomer Royal laid so much stress upon the explanation of the error of 

 radius vector, regarding it as an experiment urn crucis with respect to the value of 

 Adams's calculations, and as his views upon the matter have been much criticised, it 

 seems proper to quote the following explanatory passages which were written by him after 

 he had received Adams's letter of November 18, and when the matter was attracting 

 general attention. Writing to Sheepshanks on December 17, 1846, he says: "Concerning 

 the radius vector of Uranus, the error was certain as to sign. It was determined with 

 reasonable accuracy as to magnitude (perhaps the probable error might be or ^ of the 

 whole). Now, suppose that Adams's elements which gave longitude-corrections had given 

 a wrong sign for the correction of the radius vector, what would his theory have been 

 worth ? The alternation of signs of errors + in longitude does not exclude any other 

 hypothesis than that of an exterior planet. If the law of force differed slightly from that 

 of inverse square of the distance (of which two years ago there was great probability) 

 and if tables were calculated strictly on the law of inverse square of distance (as was 

 done in existing tables), then the discordances in longitude would have the alternate 



signs H Le Verrier evidently attached great importance to the radius vector... The 



radius vector, as you say, was to be used as an indirect verification, but its error de- 

 manded explanation quite as imperatively as the other." 



And writing to Challis, December 21, 1846, he says: 



"I am sure that you cannot have a higher opinion of Adams's ability in the 

 scientific parts of this matter than I have.... But with regard to one part of your own 

 published letter in the last Athenaeum, I must make one remark 1 . There were two 

 things to be explained, which might have existed each independently of the other, and 

 of which one could be ascertained independently of the other : viz. error of longitude and 

 error of radius vector. And there is no a priori reason for thinking that a hypothesis 



1 Challis had written: "Again, as to the error of the of the other. Mr Adams actually employed a method of 

 radius vector : it is quite impossible that its longitude calculation which required him to compute the coefficients 

 could be corrected during a period of at least 130 years of the expression for error of radius vector, before corn- 

 independently of correction of the radius vector.. ..The puting the coefficients of the expression for error of 

 investigation of one correction necessarily involves that longitude." (Athenaum, December 19, 1846.) 



