caused by atmospherical Refraction. 251 



pass across, the full effect was again produced. The reason of 

 this difference appears to be, that the quicker evaporation in- 

 creases the degree of cold, and the current brings greater dif- 

 ferences of density contiguous. 



This state of rapid evaporation will fully account for the 

 phenomenon witnessed by Mr. Latham, who has described 

 (in the Phil. Trans, for 1796, p. 357) an extraordinary eleva- 

 tion of the opposite coast of France, so as to be seen from the 

 beach at Hastings, and other parts of Sussex. 



There is a fact of the same kind stated by De la Lande, 

 (Astron. Tom. II.) who says that the mountains of Corsica 

 (though at the distance of more than 100 miles) are occa- 

 sionally visible from Genoa. 



It is probably owing to the same cause, that other objects: 

 have been sometimes seen, at such distances that we should 

 expect them to be intercepted by the curvature of the earth ; 

 for it is evident, that whensoever the evaporation over each mile 

 of surface occasions a refraction of about 1 minute, the rays 

 receive a curvature equal to that of the ocean, so that its sur- 

 face will appear flat, and the spherical form of the earth will 

 not obstruct horizontal vision of objects at any distance. 



It still remained to explain the phenomena seen by Mr. 

 Vince, as I had not hitherto made an atmosphere capable of 

 exhibiting images inverted, as well as elevated, by increased 

 density. For, in the refractions produced in the 7th, 8th, and 

 9th experiments, by evaporation at an exposed surface, I 

 observed the effect was always greatest in contact with the 

 evaporating surface; any lower point a, Fig. 9, appeared brought 

 nearer to a higher point c, by the pencil of rays from a being 

 more refracted at b, than the pencil from c was refracted at a\ 

 Therefore, any rays passing from the eye at e, as a point, through 



