") 



s. 



IV. 



Method of correcting the apparent distance of the Moon from the 

 Sun^ or a Star for the effects of Parallax and Refraction, 



BY NATHANIEL BOWDITCH, LL. D. 



HE method of correcting the apparent distance of the Moon 

 from the Sun, or a Star for the effect of parallax and refraction, 

 which was published by me in a work, entitled the ^^ Practical 

 Navigator/^ has one great advantage over other methods of ap- 

 proximation ; namely, that all the corrections are additive; which 



m 



ers it peculiarly well adapted for the 

 given without demonstration, and two c 



of mariners* It 

 i smaller correc- 



^ 



tions were neglected, as is usual in such methods. I have here 

 drawn up a general demonstration of the formula, with tatdes for 

 computing the neglected terms, from which it will appear that 

 they are generally insensible, 



.Let Z be the zenith. M the true, 



and L the apparent place of the JVfoon; 



S the true, and A the apparent place 



r 



of the Sun or Star. Upon the arch 



^ 



LA (continued if necessary) let fall the Ii/„..L 



J?"" — J 



perpendiculars MK, SB, join MB, and S 



continue it towards C to meet the perpendicular 8C let fall 

 thereon. Then in the case of the present figure, in which all 

 the angles and sides of the triangle AZL are acute, we shall 



J 



L 



have the following expression of the true distance MS. 



»^»fct*»*»^***'** 



