BROWNE'S OBSERVATION OF EGRESS, AT MOKATTAM. 293 



MICROMETER EEADINGS for the DOUBLE DIAMETER of VENUS. 



rev. 



26-971 

 26-966 

 26-998 

 26-995 

 26-987 



16-927 



rev. 



i6-gg3 



17-076 bad. 



17-013 



17-065 



17-081 



1 7-005 



17-068 



The EXTERNAL CONTACT, as far as I could judge, took place at 13 h . 50 m . 33 3 . 

 The clocks were then again compared with the transit. 



The transit being over, the three telescopes were placed so as to observe 

 the model simultaneously. The management of the mirror for illuminating 

 the model required considerable delicacy, so that Mr. Newton and I had to 

 manipulate it alternately. Our comparison was therefore made through 

 Miss Newton. Ten comparisons were made in each case ; at the conclusion 

 of which it was found that Mr. Newton recorded contact 2 S> 5, and 

 Miss Newton O s- 8, later than I did. 



If these corrections be applied to our recorded times of the actual internal 

 contact the latter would all be brought within the same second of time. The 

 application of such a correction, however, is a matter affecting other stations, 

 and cannot be done here. 



Speaking generally of the contact as seen at Mokattam it may be noticed, 

 by reference to the individual accounts, that in every case the gradual 

 formation of a black drop was perceived a little before contact, a shadow being 

 first seen between Venus and the Sun's limb, which deepened gradually until 

 a blackness nearly, if not quite, as dark as the body of the placet seemed to 

 flow over it. This was the instant noted as contact. Almost directly after 

 this each observer was perplexed by detecting light crossing the ligament, 

 which quickly became definite, till it shone out as a sharply defined silver 

 thread, which made any estimate of geometrical contact impossible. 



C. ORDE BROWNE. 



pp 2 



