C -9 1 
II. Observations on horizontal Refractions which affect the Ap- 
pearance of terrestrial Objects , and the Dip, or Depression of 
the Horizon of the Sea. By Joseph Huddart, Esq . F. R. S. 
Read November 24, 1796. 
The variation and uncertainty of the dip, in different states 
of the air, taken at the same altitude above the level of the sea, 
was the occasion of my turning my thoughts to this subject ; 
as it renders the latitude observed incorrect, by giving an er- 
roneous zenith distance of a celestial object. 
I have often observed that low lands and the extremity of 
head lands or points, forming an acute angle with the horizon 
of the sea, and viewed from a distance beyond it, appear ele- 
vated above it, with an open space between the land and the 
sea. The most remarkable instance of this appearance of the 
land I observed at Macao, for several days previous to a ty- 
phoon, in which the Locko lost her topmasts in Macao roads ; 
the points of the islands and low lands appearing the highest, 
and the spaces between them and the sea the largest, I ever 
saw. I believe it arises, and is proportional to the evaporation 
going on from the sea; and in reflecting upon this pheno- 
menon, I am convinced that those appearances must arise 
from refraction, and that instead of the density of the atmo- 
sphere increasing to the surface of the sea, it must decrease 
from some space above it ; and that evaporation is the 
