212 Olnervntions for determining 



force will carry a cubic foot of cork and a cubic foot of silver 

 with equal velocity, it must l.-e granted, that the sUver cannot 

 be revolved by the same mundiuie force in the same circle a» the 

 cork, and that if placed together (nearly as in water) one must 

 ascend towards its circle of accordant velocity, and the other 

 descend, wliich is the doctrine of Sir Richard Phillips ; and it 

 'cKplains the ph?enonicna of the descent of relatively dense bodies, 

 and the ascent of relatively rare ones, on palpable principles of 

 motion, without having recourse to any power like that of at- 

 traction, repulsion, or gravitation. 



Brentford, Sept. 5, 1820. PhU-O-VeritatiS. 



XXXIV. The Results of Of'servafions made at the Ohservatonj 

 of Trhiily College, Dublin, for determhting the Obliquity of 

 the Ecliptic, and the Maximum of the Aberration of Light, 

 By the Rev. J. Brinkley, D.D. F.R.S. andM.RJ.A. and 

 jindreto's I'rofessor of Astronomy in the University of 

 Dublin*, 



Obsekvations have been made by the eight feet circle of the 

 Observatory of Trinity College, Dublin, at the respective summer 

 solstices since the year 1S09, 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 here^ 

 tofore thought it useless to make any public communication rela- 

 tive thereto. Eut some circumstances have now induced me to 

 lay my results before the Royal Society. 



The recent publication of Mr. Bessel's valuable labours on the 

 observations of Dr. Bradley, has afforded us a more exact deter- 

 mination of the obliquity of the ecliptic, as deduced from the 

 early observations by the Greenwich quadrant, than we before 

 possessed. The comparison of this with the present obliquity, 

 gives us the diminution for an interval of nearly 60 years, with 

 B considerable degree of accuracy, and almost sufficient to en- 

 able us to state with some confidence the mass of Venus. 



To obtain this pointwith a greater degree of certainty, the pre- 

 sent obliquitv, as deduced from a mean of the observations of dif- 

 ferent astronomers, should bp used. 



It has l)eeii an opinion almost generally received among astro- 

 nomers, that observations of the winter solstice have given a 

 less obliquity of the ecliptic than observations of the summer sol» 

 stice. 



The explanation of this seemed very difficult. But in the 

 above»;nenlioned work of Mr. Bessel, he calls in question this 



* From Phil, Trans. Royal Soc. fpr 1819, Part. II. 



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