37 
on Horizontal Refractions. 
Respecting the appearance of the Abbey Head before men- 
tioned, fig. i, the dotted line AB represents the limit, or the 
lowest points of the land that can be seen over the sea ; for, as 
above stated, all the objects appearing below this line, are the 
land above it inverted ; and where the land is low, as at d and 
m, it must appear elevated above the horizon of the sea. 
In fig. 5. let H O represent the curve of the ocean, and d the 
extreme top of the mount visible at A by the help of refraction ; 
the dotted pencil of rays c c passing from d to the eye in some 
part a little below the maximum of density, where inversion 
begins ; therefore no land lower than this can be seen ; for any 
pencil from a point in the land lower than this, must in the 
refraction have a contrary flexure in the curve, and there- 
fore pass above the observer. Let AD be a tangent to the 
curve at A, then the object d will appear to be elevated by re- 
fraction to D ; also let A v be a tangent to the pencil A a: at A, 
then the angle D A x will appear to be an open space, or be- 
tween D and the horizon of the sea. Suppose a star should ap- 
pear very near and over the mount d, as at *, two pencils would 
issue from every point of it, and form a star below as well as 
above the hummock d. There are always confused or ill defined 
images of the objects at the height of the dotted line, fig. 1, 
above the level of the sea, as before mentioned ; and instead of 
the points of d ending sharp in that line, they appear blunted, 
and the Abbey Head is frequently insulated at the neck m. 
I have viewed, from an elevated situation, a point or head 
land at a distance beyond the horizon of the sea, forming, as 
in fig. 6. a straight line A B, making an acute angle B AO with 
the horizon of the sea. Seeing the extreme point blunted and 
elevated, I descended; and though in descending the horizon 
