The Rev. Dr. Robinson on the Constant of Refraction. 



201 



30 X 6?R = — S0".59 dvi= — 1".02 



K = 4.2046 dfx=— 0.242 



a Cygni. 



Twenty- four observations (1838. 105) give, 



*8 = _j_44°40'35".50. 



Precession = -j- 12". .597 ; sec var. = -\- 0".226 ; proper motion Insensible. 



