an unusual horizontal Refraction of the Air. 19 
the hulk below the horizon xy , passing by the same cliffs AB ; 
an inverted image D of which appeared against the cliffs, as re- 
presented in fig. 6 . The ship was in motion, and remained at 
the same distance on the other side of the horizon : I conti- 
nued my observations upon it till it had passed the cliffs for a 
considerable distance, but there was no change of appearance. 
The cliffs were illuminated by the sun, and appeared very dis- 
tinctly ; but there was no image above, as in the last case. 
Continuing to observe the same cliffs AB, fig. 7 , 1 soon after 
discovered two partial elevations m, n , of the sea, by the un- 
usual refraction; they changed their figures a little, and dis- 
appeared in the place where they first appeared, and were 
equally distinct in every part. 
About this time, I observed a very thick fog coming upon the 
horizon from the other side, rolling upon it with a prodigious 
velocity; curling as it went along, like volumes of smoke some- 
times out of a chimney. This appeared several times. I con- 
clude, therefore, that there was a considerable fog on the other 
side of the horizon. 
The last phamomenon which I observed was that which is 
represented in fig. 8 ; where xy represents the horizon, a b two 
partial elevations of the sea, meeting at c, and continued to d ; 
e , another partial elevation of the sea, of which kind I observed 
several, some of which moved parallel to the horizon, with a 
very great velocity. I conjecture, therefore, that these appear- 
ances were, in part at least, caused by the fog on the other side 
of the horizon. For, though I did not at the same time see the 
motion of these images and that of the fog, yet, from memory, 
I judged the motions to be equal; and they were also in the 
same direction. A fog which, by producing an unusual refrac- 
D 2 
