C 122 3 
IX. Corrections to the reductions of Lieutenant Foster's Ob¬ 
servations on Atmospherical Refractions at Port Bowen; with 
Addenda to the Table of Magnetic Intensities at the same 
place. By Lieutenant Henry Foster, R. JV'. F. R. S. 
Read March 22, 1827. 
I HASTEN to acquaint the Royal Society with an error I have 
inadvertently committed in my observations on Atmospheri¬ 
cal Refractions at Port Bowen, published in Part IV. of the 
Philosophical Transactions for 1826. The error alluded to 
arises from my having used an erroneous value of the divi¬ 
sions on the long level of the repeating circle, with which the 
observations were made. For the detection of this error, I 
am indebted to Captain Kater, who recently having had 
occasion to use the same instrument, found the value of each 
division of the level to be more than ten seconds in arc, of 
which he very kindly informed me, knowing that I had con¬ 
sidered them as equal to single seconds only; and at the same 
time he wished me to acquaint him, if any accident had hap¬ 
pened to the instrument, by which the level might have been 
changed. I knew that no accident had befallen the in¬ 
strument, and that the level was the same which I had used ; 
I therefore immediately proceeded to town, and in Captain 
Kater's presence ascertained the value of each division of 
the level to be io".9. 
In order to explain the source of the error into which I 
have fallen, I must state, that on receiving the repeating 
