6o . Oh/ervations upon an ttnufual 



nued to d: e, another partial elevation of the fea, of which kind 

 I obferved feveral, feme of which moved parallel to the hori- 

 zon with a very great velocity. I conje6ture, therefore, that 

 thefe appearances were, in part at leaft, caufed by the fog on 

 the other fide of the horizon. For, though I did not at the 

 fame time fee the motion of thefe images and that of the 

 fog, yet, from memory, I judged the motions to be equal j 

 and they were alfo in the fame direction. A fog which, by 

 producing an unufual refraftion, might form ihele images, 

 would, by its motion, produce a correfpondlng motion of 

 the images. 



I have here defcribed all the different pha&nomena which 

 I obferved from the unufual refraction, of mod of which I 

 faw a great many inftances. Every fliip which I obferved 

 on the other fide of the horizon of the fea, exhibited phae- 

 nomena of the kind here defcribed, but not in the fame de-- 

 gree. Of two fliips which, in different parts, were equally 

 funk below the horizon, the inverted image of one would 

 but juft begin to appear, whilft that of the other would re- 

 prefent nearly the whole of the fliip. But this I obferved, in 

 general, that as the Ihip gradually defcended below the hori- 

 zon, more of the image gradually appeared, and it afcended ; 

 and the contrary, when the fliips were afcending. Upon the 

 horizon, in different parts, one fliip 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 frequently appeared 

 as clear and (liarp as the fliips themfclves, and of the fame 

 magnitude. Of the fliips on this fide of the horizon, no 

 phoenomena of this kind appeared. There was no fog upon 

 our coaft , and the fhips in the Downs, and the South Fore- 

 land, exhibited no uncommon appearances. The ufual re- 

 fradion at the fame time was uncommonly great j for the 

 tide was high, and at the very edge of the water I could fee. 

 the clitfs at Calais a very confiderable height above the hori- 

 zon; whereas they are frequently not to be feen in clear 

 weather from the high lands about the place. The French 

 coaft alfo appeared both ways, to a much greater diftance 



than 



