ifie Olliquihj of the Ecliptic, &?c. 213 



opinion, and shows that the observations of Dr, Bradley give 

 the same result botli in snmnier and winter. His own observa- 

 tions also tend to the ^ame conclnsion. The observations of Dr. 

 Maskelvne, of M. Oriani, of M. Arago, and of Mr. Pond, are in 

 opposition to these ; to vvhicli mvown maybe added. 



It is not likely that this difference really exists; but it is a ques- 

 tion of some importance in astronomy, and the explanation 

 thereof may throw some light on other points. 



It is probable the difference arises from some unknown modifi- 

 cation of refraction. I find, and I believe other observers have 

 found the same, that at the winter solstice, an irregularity of re- 

 fraction takes place for the sun greater than for the stars, at the 

 same zenith distance. The zenith distance of the sun at this 

 place is then nearly 77' • 



What Mr. Bessel has adduced certainly tends to render the 

 prevalent opinion doubtful. It therefore appears to me of ron> 

 f equence, that astronomers should pay attention to the observa- 

 tions at tlie winter solstice. My observations at that time have 

 been much fewer than in the summer, because, on account of 

 the uncertainty of refraction, I considered them of less im- 

 portance. 



It has been proposed to make the two results agree, by an in- 

 crease of the quantity of Bradley's mean refraction ; but this 

 could not be done without increasing it by a quantity greater 

 than can be justified by other determinations respecting refrac- 

 tion. 



Considering then this uncertainty respecting the observations 

 of the winter solstice, it appears better to compare the results 

 from Dr. Bradley's summer solstices, with the result as deduced 

 from the mean of the observations of different astronomers. 



Mean OlliquHy, Jan. I, 1813. 



l\I. Oriani* 4 sunnner solstices 



Mr. Pondf 2 summer solstices 



Mr.AragoJ 2 summer solstices 



Dr. Brinkley ' 8 summer solstices 



23" 27' 50",34 



23 27 50 ,37 



23 27 50 ,09 



23 27 50 ,99 



Mean Jan. I. 1813 23 27 50 ,45' 



Dr. Bradley, Jan. 1. 1755 23 28 15 ,49 



diff. 58 years. 25 ,0^ 



This givts 0," 43, for the annual diminution. 



* Sec Mr. Bessel's work, p. 62. 



t IMiil. Trans. ISliJ, p.30-1. This is corrcctrd for the solar nutation. 



♦ Conn, dci Tempt, Idip, The obscrv4tiu:i3 were made with a three 

 feet rc|icating circjet 



The 



