14 Mr Blackadder on Vertical and Lateral Mirage. 



formed of huge blocks of cut sand-stone, and was intended 

 both as a protection against the sea, and, if need should be, 

 against the attacks of an enemy. When the weather is favour- 

 able, this bulwark affords an opportunity of witnessing most 

 of the interesting phenomena, connected with what has been 

 termed unusual atmospheric refraction. Near the centre of 

 the range there is a solid stone tower, and from this to the 

 eastern extremity, the appearances are observed to most ad- 

 vantage. 



From the tower eastward, the bulwark forms a straight 

 line to the distance of about 498 feet. It is eight feet in 

 height, on the side next to the land, and has a foot-way up- 

 wards of two feet in breadth, and about three feet from the 

 ground. At the top, the parapet is three feet wide, and has a 

 slight inclination towards the sea. 



When the weather is favourable, and that is not of rare oc- 

 currence, the top of the parapet has the appearance of a mir- 

 ror, or rather of a sheet of ice, and, if in this state, another 

 person stands or walks upon it, at a little distance, an inverted 

 image is seen under him. If, while standing on the foot-way, 

 another person stands on it also, but at some distance, with his 

 face turned towards the sea, his image will appear oppo- 

 site to him, giving the appearance of two persons talking, 

 or saluting each other. If again, when standing on the foot- 

 way, and looking in a direction from the tower, another per- 

 son crosses the eastern extremity of the bulwark, passing 

 through the water-gate, either to or from the sea, there is pro- 

 duced the appearance of two persons moving in opposite di- 

 rections — constituting what has been termed a lateral mirage — 

 first one is seen moving past, and then the other in an oppo- 

 site direction, with some interval between them. In looking 

 over the parapet, distant objects are seen variously modified, 

 the mountains converted into immense bridges, &c. 



On going to the eastern extremity of the bulwark, and di- 

 recting the eye towards the tower, the latter appears curious- 

 ly modified, part of it being as it were cut off, and brought 

 down, so as to form another small and elegant tower, in the 

 form of certain sepulchral monuments. See Plate I. Fig. 13. 



