28] NOTE ON THE CONSTANT OF LUNAR PARALLAX. 227 



then the constant term of the sine of the horizontal parallax corresponding 

 to the latitude just specified may be represented by 



/ M R\ k F 



\M+m ' P) ' 



and therefore the constant term of the sine of the equatorial horizontal 

 parallax may be represented by 



A I M R* I M A 3 \* 

 R \M+m "PI (if+rn ' R'P) ' 



where F is a factor which may be found by theory from elements which 

 may be considered as known with all desirable accuracy. 



M 



The values of , A, R and P employed in finding my constant are 



the following : 



^=81-5, 



TO 



which corresponds very nearly to Dr Peters' constant of Nutation ; 



A = 20923505 English feet, 

 # = 20900320 

 P= 3-256989 



R and P belong to a point the sine of the geographical latitude of 



which is -T- . 



Vo 



A and R are the quantities found from Bessel's latest determination 

 of the figure and dimensions of the Earth as given in Astron. Nachr., 

 Vol. xix., p. 216, supposing that 



1 Toise = 6-394564 English feet. 



P is found thus : according to the formula given in p. 94 of Baily's 

 Report on Foster's Pendulum experiments, (Mem. of the Roy. Astr. Soc., 

 Vol. VIL), the square of the number of vibrations made in a mean solar 



day, at a point the sine of whose geographical latitude is -j- , by a pendulum 



v<* 



which vibrates seconds in London is 



7441625711 +1 (38286335) = 7454387823. 

 o 



292 



