v n t i c l i: v 1 1 



Investigations which led to the detection of the coincidence between the computed place oj the 

 Vianet Levcrrier, and the observed place of a Star recorded by Lalande, in May, 1795. 

 By Sears C. Walker. Read February 19/A, 18 17. 



Washington, D. C, February 18th, 1847. 

 To Dr. Robert M. Patterson: 



My Dear Sir, — I hasten to comply with the invitation in your letter of yesterday to 

 lay before the American Philosophical Society the steps that led to the detection of the 

 very remarkable coincidence between the computed place of the planet Levcrrier and the 

 observed place of a star of the 7.8 magnitude, which passed the meridian of Paris at 

 1 1//. 11m. 23s.5 of Lalandc's clock time, May 10th, 1795. 



Soon after the arrival of the news of the physical discovery of Levcrrier, a suggestion, 

 by Mr. E. C. Herrick, of its possible identity with the Wartman planet of 1831, induced 

 me to commence the search for the approximate elements of the two. I soon came to the 

 conclusion that Levcrrier could not have been in Wartman's region in 1831, and that no 

 satisfactory orbit could be found for Wartman's planet, from the imperfect tracing of its 

 path in the Contcs Rendus for 183G. 



In this first inquiry concerning the motions of Levcrrier, I learned the near approach of 

 its orbit to the circular form. The same analogies of the solar system that furnished 

 Levcrrier and Adams the clue to their analytical discovery of the planet, were to be the 

 -aides in the first attempt to sketch its orbit. 



It was naturally to be presumed that the inclination and eccentricity of this primary 

 planet were small, and that with a radius vector nearly twice that of Ilerschel, the sun's 

 power to impress daily variation- of the radius sector, and orbital motion must be com- 

 paratively small, and that in a first approximation these daily variations, as well as their 

 first and second differences, might be neglected. 



Accordingly, I commenced with the simple hypothesis of constancy of the radius vector, 

 from September 2(ith, to November 21st, a period of fifty-etgbl days, leaving the charac- 

 ter of the orbit, whether nearly circular or much flattened, to be the result of the investi- 

 gation. 



w.i . t. — :'»."> 



