VOL. LXXXIX.J PHILOSOPHICAL TRANSACTIONS. 439 



sents the horizon of the sea, ab the cliffs, ab their image, and vw the image of 

 the sea between them: the depth of ab was much less than that of ab. It is pro- 

 bable however, that vw might not be the image of the sea immediately adjoining 

 to the cliffs, but a partial elevation of the sea at some distance from them ; and 

 that the image vw might intercept some part of the image ab, which would other- 

 wise have been visible; we must not therefore conclude that the image ab, so far as 

 it appeared, was less than the corresponding part of the object. From the memo- 

 randums which I made at the time of observation, I do not find that I examined 

 the appearance of the cliff ab, and its image ab; which, had there at that time been 

 any striking marks in them, would have determined whether the object and its 

 image were of the same magnitude. The image ab was however erect; the boun- 

 daries on the top of ab and ab agreeing together. Having examined this for some 

 time, and taken a drawing of the appearance, during which I could discover no 

 variation, I directed my telescope to other objects; and on turning it again to the 

 same cliffs, after the space of about 6 or 7 minutes, the images ab and vw were 

 vanished ; but examining them again soon after, the images were again visible, and 

 in every respect the same as they appeared before. A short time after they disap- 

 peared, and did not appear any more. 



Soon after the above appearances, I observed a ship c, with the hull below the 

 horizon xy, passing by the same cliffs ab ; an inverted image d of which appeared 

 against the cliffs, as represented in fig. 6. The ship was in motion, and remained 

 at the same distance on the other side of the horizon : I continued my observations 

 on 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 

 distinctly; but there was no image above, as in the last case. Continuing to ob- 

 serve the same cliffs ab, fig. 7, I soon after discovered 2 partial elevations m, n, of 

 the sea, by the unusual refraction ; they changed their figures a little, and disap- 

 peared in the place where they first appeared, and were equally distinct in every part. 

 About this time, I observed a very thick fog coming on the horizon from the 

 other side, rolling on it with a prodigious velocity; curling as it went along, like 

 volumes of smoke sometimes out of a chimney. This appeared several times. I 

 conclude therefore, that there was a considerable fog on the other side of the ho- 

 rizon. The last phenomenon observed was that represented in fig. 8; where xy 

 represents the horizon, ab 2 partial elevations of the sea, meeting at c, and conti- 

 nued 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 con- 

 jecture therefore, that these appearances 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 refraction, might form these images, would, by its motion, produce a 

 corresponding motion of the images. 



