EQUATIONS OF DISTANCE OF CENTERS, FOR MOKATTAM. 301 



COLLECTED EQUATIONS, FROM ALL OBSERVATIONS AT MOKATTAM. 



The observations at Mokattam yield therefore the following FINAL 

 EQUATIONS : 



(1) The Micrometric Measures of distance of Limbs 



o = 4"-g3 + "-i85i n + -1678 8 E.A. + -9821 8 N.P.D. "-0289 8 t + 8 R 2-i83 8 r ; 



(2) Mr. Newton's Internal Contact 



o = 4"-o6 + "-2014 n + -2434 8 E.A. + -9646 8 N.P.D. "-0342 8 t + 8 R 8 r; 



(3) Miss Newton's Internal Contact 



o = 3"-g8 + "-2014 n + -2436 8 R.A. + -9645 8 N.P.D. "-0342 8 t + & R 8 r ; 



(4) Captain Browne's Internal Contact 



o = 3"-g5 + "-2oi5 n + -2436 8 E.A. + -9646 8 N.P.D. "-0342 8 t + 8 E 8 r; 



(5) The Micrometric Measures of distance of Cusps 



o = 4"-36 + "-2044 n + -2899 8 E.A. + -g5g5 8 N.P.D. "-o353 8 t + 8 E o'66g 8 r; 



(6) Captain Browne's External Contact 



o = 4"-34 + "'2149 n + -3325 8 E.A. + -g328 8 N.P.D. "-0402 8 < + 8 R + 8 r ; 



(7) Miss Newton's External Contact 



o = 3"'6o + "-2149 n + -3334 8 E.A. + ^24 8 N.P.D. "-0402 8 t + 8 E + 8 r ; 



(8) Mr. Newton's External Contact 



o = 3"-2i + "-2i5o n + -333g 8 E.A. + -g322 8 N.P.D. "-0402 8 t + 8 E + 8 r. 



On page 288 the final longitude of Mokattam is stated to be 2 h . 5 m . 6 s -24, E., 

 hence the above Equations require the correction obtained by making 8 t 

 = + s -34. It will be understood that 8 R.A. and 3 N.P.D. are the cor- 

 rections required to Tabular R.A. and N.P.D. of Venus in seconds of arc 

 referred to the center of the Sun. 



After his return to England, Captain Browne made a determination of the 

 value of a revolution of the screw of his double-image micrometer. The 

 telescope was laid horizontally upon two tripod supports, and directed upon 

 the transit instrument which had been used at Mokattam. A fixed web had 

 been inserted in the transit-instrument in addition to the five webs moved by 

 the micrometer-screw. In the focus of the eye-lens of the double-image 

 micrometer were inserted two webs crossed. The reticule of the transit being 

 sharply defined in the field of the double-image micrometer, the distance of 

 the fixed web from the center movable web was measured by bringing their 

 images into coincidence with the screw of the double-image micrometer, near 

 the center of the field as defined by the crossed webs. In this manner, 



QQ 2 



