C 206 3 
IX. Observations to determine the amount of Atmospherical Re- 
fraction at Port Bowen in the Tears 1824-25. By Captain 
W. E. Parry, R. N. F. R. S. Lieutenant Henry Foster, 
R. JV\ F. R. S. a?id Lieutenant J. C. Ross, R. JV*. F. L. S. 
T o ascertain correctly by actual observation the amount of 
atmospherical refraction at low altitudes and at various states 
of the barometer and thermometer, is a problem which has 
long occupied the attention of practical astronomers; and 
many elaborate theories have also been given to explain the 
anomalies which have hitherto attended the most careful ob- 
servations. 
In Mr. Ivory’s Paper, printed in the Philosophical Trans- 
actions for 1823, he states (page 495), that his table of re- 
fractions has been constructed merely with the view of com- 
paring the theory in the paper with observation. He adds, 
however, “ that it would be more satisfactory to determine 
“ the same quantity (/) by the comparison of many observed 
“ refractions at low altitudes between the distances of 85 
“ and 88 degrees from the zenith; and by this means a 
“ table might be constructed that would be deserving of 
e: greater confidence/* 
With a view, therefore, to supply the desideratum alluded 
to, three distinct series of observations were made at Port 
Bowen, by Captain Parry, Lieutenant Foster, and Lieutenant 
Ross ; the details of which are given in the following Paper. 
Various methods suggested themselves for the determina- 
tion of this question. The first was to measure the zenith 
distance of kno wn stars at a given moment, with the repeat- 
