Astronomy 583 



The representation of the observations by tne concluded 

 theory will probably be regarded as good. The mean out- 

 standing difference during each five years since the discovery 

 of the planet only exceeds a second of arc in a single in- 

 stance — namely, during the years 1822-26, when it amounts 

 to i". \} 



"This agreement is very much better than any obtained 

 before. Still, the vast number of observations used, and the 

 care taken to reduce them to a uniform standard, led me to 

 believe a better representation possible ; and the outstand- 

 ing differences, minute though they be, follow a regular law, 

 thus showing that they do not arise from the purely accidental 

 errors of observation. How far they arise from errors in my 

 own theoretical computations, how far from the reductions of 

 the observations themselves, and how far from the unavoid- 

 able errors of the instruments, I am unable to say without 

 further investigation. It would be desirable to learn whether 

 they may be due to the action of a trans- Neptunian planet, 

 but to do this would require an entire re- reduction of all the 

 older observations. Such a work is on many accounts an 

 astronomical desideratum ; but it could not be undertaken 

 except under the auspices of the government. 



" In the eighth chapter the general formulae and elements 

 are collected and expressed in the form most convenient for 

 permanent use. 



"The ninth, and concluding, chapter gives the tables by 

 which the position of the planet may be computed for any 

 time between the Christian era and the year 2300."^ 



Professor Newcomb's later works on planetary theory are 

 mostly printed in the volumes of Memoirs printed by the 

 "American Ephemeris."^ 



1 The angular diameter of Uranus is about and Nautical Almanac " from 1857 till 1897. 



4". E. S. H. He entered the United States Xa\-j' in the 



- "Smithsonian Report," 1872, page 25. first named year as computer on the Alma- 



3 It is interesting to mention in this connec- nac, and became its Superintendent in 1877, 



tion that Professor Newcomb was connected in which capacity he continued until his re- 



with the office of the " American Ephemeris lirement. 



