148 PROCEEDINGS OF THE AMERICAN ACADEMY 



" I do not recollect a closer agreement of an orbit with actual obser- 

 vation. Accordingly I regard Elements V. as the present disturbed 

 elements of Neptune. 



" You will notice that the values of e and n came out nearly the same 

 as those of Elements III., required by the hypothesis of identity of the 

 planet and missing star of the Histoire Celeste, May 10th, 1795, The 

 node and inclination are so connected together at present that (very 

 nearly) ten times the increase of the latter applied to the former leaves 

 the geocentric place unchanged. 



" Let us make the hypothetical Elements VI. by applying to (V.) the 

 corrections /j Q, = -\- 8".50, and // 1 = -|- 84".8, and let us suppose that 

 the term T.2 8 {n t) has increased 0".03422 in the last fifty-two years; 

 then Elements VI. will represent the last nine months' observations, 

 and place the star and planet together May 10th, 1795. 



" I am engaged in computing the constant coefficients for the pertur- 

 bations of Neptune on your hypothesis of (2 n^"" — n ^'•) =-■ 0, or in 

 other words of the applicability of the Laplacian libration first pointed 

 out by yourself. As far as I am at present informed, the near ap- 

 proach of this expression to was first noticed by ourselves, on the 

 occasion of your visit to Washington, on the 25th of February last. 



" A glance at the configurations of the planets for the last two or three 

 years would serve to indicate that while Saturn and Uranus are still 

 increasing the term ~ .2" 5 (n t), Jupiter has produced a tide (if I may 

 use the phrase) which has not yet subsided, and which, added to the 

 action of the other two, may have increased the disturbed daily motion 

 0".32 above the pure elliptic value. In this case, your period is estab- 

 lished. 



" Both hypotheses, that of the identity of the star and planet, and of 

 the libration of Neptune's year round the double of that of Uranus, 

 are now rendered so probable by conclusions from direct observations, 

 that nothing but a rigorous computation of the perturbations of Nep- 

 tune can throw any farther light on the subject at present. I shall 

 look with anxiety for the publication of your researches on this subject. 



" Yours truly, 



" Sears C. Walker." 



After reading this letter, Professor Peirce remarked that Mr. 

 Walker's discovery of the identity of Neptune and the star of 

 Lalande was indisputably confirmed by an examination which 

 Mr. Mauvais of the Paris Observatory had made into the orig- 



