VOL. LXXVII.] PHILOSOPHICAL TRANSACTIONS. 303 



in the works of the East-Indian natwralists. I have only met with one Chinese 

 drawing, in the library of Sir Joseph Banks, Bart. p. r. s. among some others of 

 their garden plants, that seems to represent the present. It is said to be called 

 Chu-Lan by the Chinese ; but it ought not to be confounded with the Tsjiulang 

 or Camunium Chinense of Rumphius (Herb. Amboin. 1. 7, cap. 15, and Auc- 

 tuarii ejusd. cap. 47,) the description of which seems to correspond in some 

 parts with the Chloranthus : the first figure however, on the 18th plate, shows 

 the plant of Rumphius to be the Vitex pinnata of Linnaeus. 



XXXVl. On the Precession of the Equinoxes. By the Rev. Sam. F'ince, M. A., 



F. R. S, p. 363. 



1 . The true cause of the precession of the equinoctial points was first assigned 

 by Sir Isaac Newton ; but it is confessed, that he has fallen into an error in his 

 investigation of the effect. Without however entering into any inquiry relative 

 to the circumstances in which he has erred, I propose to show how we may ob- 

 tain a true solution from his own principles, by means of which alone the whole 

 calculation may be rendered extremely simple and evident; and though very sa- 

 tisfactory solutions have been already given, yet the importance of the problem 

 will sufficiently apologize for offering any thing further on the subject that may 

 at all tend to elucidate it. 



2. Let s (pi. 4, fig. l) be the sun, abdc the earth, t its centre, Ea the 

 equator, v,p, the poles; draw ctb perpendicular to sad, and join se, which 

 produce to meet cb in k. Call the radius et unity, and let the force of the sun 

 on a particle at t be — 5, then the force on a particle at e = — -; hence, if we 



resolve this latter force into 1 others, one in the direction et, and the other in 

 the direction parallel to ts, we have se : st :: 



— - : the force in the direction parallel to ts = — -.•=■ r-. = — -A , 



SE* '^ SE^ (ST — EK)* ST^ ' ST3 ' 



omitting the other terms of the series on account of their smallness. Hence 



, 3ek 



the force with which a particle at e is drawn from cb is equal to — ;conse' 



quently the effect of this force in a direction perpendicular to et will be 



EK X KT i^gj^^g |.j^jg force : the force of the sun on a particle at t :: x k t 



ST^ i ST? 



: — J :: 3ek X kt : st. Now if p = the periodic time of the earth, p = the 



periodic time of a body revolving at the earth's surface; then the force of the 

 earth to the sun : the force of the body to the earth, or the force of gravity, :: 



— : -^ ; and hence the force of the sun on a particle at e perpendicular to et ; 



,r ^ r c '4. 3eK X kt X P* , 



ttie force of gravity :: 7 — : K 



