5. 



NEISON'S LUNAR INEQUALITY. 



DIARY, 1877, August 13. "In the course of the day while in the 

 train and also while walking about in London thought out a way of 

 deriving a very approximate value of the coefficient of Neison's inequality 

 due to Jupiter from the coefficient of the Lunar Evection." 



In a comparison of Hansen's "Tables de la Lune" with observations 

 made at Greenwich and Washington, Professor Newcomb discovered an 

 inequality of eccentricity and longitude of perigee which may be expressed* 



= + 0"75sin7V, 



de 75 cos jV, 

 where 



N=253-2 + 2l-6(t- 1868'l). 



The explanation of this was found by Mr Neison, whose researches 

 revealed an inequality due to the action of Jupiter 



81= 2"-2Qsm(2m-2J), 

 eSz3-= '5 8 sin (2w - 2 J), 



8e=-0 58cos(2n7-2J"), 

 and 



* See Hon. Not. xxxvn., p. 428. 



