20 Mr. Vince's Observations upon 
tion, might form these images, would, by its motion, produce 
a corresponding motion of the images. 
I have here described all the different phsenomena which 
I observed from the unusual refraction, of most of which I saw 
a great many instances. Every ship which 1 observed on the 
other side of the horizon of the sea, exhibited phsenomena of the 
kind here described, but not in the same degree. Of two ships 
which, in different parts, were equally sunk below the horizon, 
the inverted image of one would but just begin to appear, 
whilst that of the other would represent nearly the whole of the 
ship. But this I observed, in general, that as the ship gradu- 
ally descended below the horizon, more of the image gradually 
appeared, and it ascended; and the contrary, when the ships 
were ascending. Upon the horizon, in different parts, one ship 
would have a complete inverted image ; another would have 
only a partial image ; and a third would have no image at all. 
The images were in general extremely well defined ; and fre- 
quently appeared as clear and sharp as the ships themselves, 
and of the same magnitude. Of the ships on this side of the 
horizon, no phsenomena of this kind appeared. There was no 
fog upon our coast; and the ships in the Downs, and the 
South Foreland, exhibited no uncommon appearances. The 
usual refraction at the same time was uncommonly great ; for 
the tide was high, and at the very edge of the water I could see 
the cliffs at Calais a very considerable height above the horizon; 
whereas they are frequently not to be seen in clear weather 
from the high lands about the place. The French coast also 
appeared both ways, to a much greater distance than I ever ob- 
served it at any other time ; particularly towards the east, on 
which part also the unusual refraction was the strongest. 
