242 Dr. Brinkley’s observations for determining 
the present obliquity, as deduced from a mean of the obser^ 
vations of different astronomers, should be used. 
It has been an opinion almost generally received among 
astronomers, that observations of the winter solstice, have 
given a less obliquity of the ecliptic than observations of the 
summer solstice. 
The explanation of this seemed very difficult. But in the 
above mentioned work of Mr. Bessel, he calls in question 
this opinion, and shows that the observations of Dr. Bradley 
give the same result, both in summer and winter. His own 
observations also tend to the same conclusion. The observa- 
tions of Dr. Maskelyne, of M. Oriani, of M. Arago, and of 
Mr. Pond, are in opposition to these ; to which my own may 
be added. 
It is not likely that this difference really exists, but it is 
a question of some importance in astronomy, and the ex- 
planation thereof may throw some light on other points. 
It is probable the difference arises from some unknown 
modification of refraction. I find, and I believe other obser- 
vers have found the same, that at the winter solstice, an irre- 
gularity of refraction 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 0 . 
What Mr. Bessel has adduced, certainly tends to render 
the prevalent opinion doubtful. It therefore appears to me 
of consequence, that astronomers should pay attention to the 
observations at the 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 importance. 
y 
