390 ACCOUNT OF AN OPTICAL ILLUSION, &;C. 
objects. Hence we may probably explain the appearances 
I have mentioned, being refi acted in curves from the oppo- 
site coast, just as the siiipping and buildings on the shore 
of Naples have sometimes appeared from Messina floating 
inverted in the atmosphere. I am Sir, your very obedient 
servant, Sami-. Thos. Gregg. 
P. S. — Mr Gregg's family are Quakers, and their vera- 
city may be depended on. I am not, however, exactly cer- 
tain whether these appearances could be reconciled with 
the theory laid down, taking into consideration the geogra- 
phical position of the Islands, and the situation of the sun 
at 5 o'clock p. M. ; but, as the sailors state that they only 
occur with east and north-east winds, they would seem to 
depend more on this cause than any other, and this would 
obviate any objections that might arise from the position of 
the sun at 5 o'clock. Mr Gregg is a medical student. 
R. Stewart. 
