SOLAR ECLIPSE OF MAY 14, 15, 1836. 383 



altitudes of the moon in northern, contrasted with those made in 

 southern parallels of terrestrial latitude. The value of d ts, or 

 the correction of Burckhardt's constant of parallax, as found bj Mr 

 Walker, is -\- 1"-516. Burckhardt's constant is 51' 0"-5, making, 

 when this correction is applied, 57' S"-0. It appears from Mr Hen- 

 derson's memoir on the Constant Quantity of the Moon's Equatorial 

 Horizontal Parallax, (see Memoirs of the Rojal Astronomical Society, 

 vol. 10, p. 294,) in which he has discussed an extensive series of me- 

 ridian observations of 1832 and 1833, with mural circles, at Green- 

 wich, Cambridge and the Cape of Good Hope, that the value of this 

 constant is 57' l"-8. 



It is seldom that solar eclipses have been accurately observed over 

 a portion of the earth's surface large enough to admit of the coeffi- 

 cient of parallax thus changing its sign; occultations of planets and 

 stars of the first magnitude can hardly be expected to furnish equa- 

 tions of condition capable of determining the constant of the moon's 

 parallax with precision. The difficulty of locating observers at con- 

 venient places for this purpose, and the uncertainty concerning the 

 precise instant of an immersion or emersion at the moon's bright limb, 

 must continue to furnish obstacles nearly insuperable. The impor- 

 tance, therefore, of MrRumker's paper is much enhanced by the rare 

 opportunity which it affords. For the purpose of comparison, the prin- 

 cipal values of the moon's horizontal equatorial parallax, yet obtained, 

 are here collected together. They are found chiefly in Mr Hender- 

 son's Memoir. They are as follows : 



57' 0""00 Biirff, from Laplace's formulae, moon's mass of the earth's. 



'^ ^ G8-5 



57' l"-00 Burg, in his lunar tables. 



57' 0"'50 Burckhardt, from Laplace's theory. 



57' 0"*90 Damoiseau, from the same, usinff for moon's mass 



74 



57' 3"'10 Plana, Theorie de la Lu,ne, usinff for moon's mass — 



^ 87 



57' 2"'0O Henderson, from the same, using 9"'25 for the coeflicient of lunar nutation, 



which gives, for moon's mass, — - . 

 & 79-9 



57' 4"-60 La Caille "^ t:, „ . . , ... .^ „ ... 



, , „,, „^ X , , ! From European observations compared vvuh those 01 La V-'aille, at 



57 3"-70 Laland ' . - ^ - - . ._ r 



57' 6"-00 DuSejour 

 TI. 4 V 



f the Cape of Good Hope. 

 J 



