c 241 : 
XVII. The results of Observations made at the Observatory of 
Trinity College , Dublin, for determining the Obliquity of the 
Ecliptic, and the Maximum of the Aberration of Light. By the 
Rev. J. Brinkley, D. D. F. R. S. and M. R. I. A. and An- 
drew’s Professor of Astronomy in the University of Dublin. 
Read April 1, 1819. 
Observations have been made by the eight feet circle 
of the Observatory of Trinity College, Dublin, at the respec- 
tive summer solstices since the year 1809, with the exception 
of two. The obliquity of the ecliptic thence resulting, has 
always agreed so nearly with that adopted in the French 
tables, that I have heretofore thought it useless to make any 
public communication relative thereto. But some circum- 
stances have now induced me to lay my results before the 
Royal Society. 
The recent publication of Mr. Bessei/s valuable labours on 
the observations of Dr. Bradley, has afforded us a more 
exact determination of the obliquity of the ecliptic, as de- 
duced from the early observations by the Greenwich qua- 
drant, than we before possessed. The comparison of this 
with the present obliquity, gives us the diminution for an 
interval of nearly 60 years, with a considerable degree of ac- 
curacy, and almost sufficient to enable us to state with some 
confidence the mass of Venus. 
To obtain this point with a greater degree of certainty, 
mdcccxix. I i 
