356 On the Colour of the Atmosphere and Deep Water. 



dipt into a blue tincture ; the immersed part is bright and co- 

 loured, while that out of the water is obscure and retains its lo- 

 cal colour. 



The landing-place is at the end of the grotto, on a small 

 space level with the water, formed by the rock ; it is the only 

 spot in the grotto that could be supposed to be the work of hu- 

 man hands. The spectator then ascends to a second ledge of 

 rock, about three feet in elevation, and forming a commodious 

 station for several persons : it is from this point that the pheno- 

 mena presented by the azure grotto are best observed *. 



The small entrance admits a stream of white light, which re- 

 sembles the reflection of the rising moon from the surface of the 

 sea, and reaches to the middle of the sheet of water; all the rest 

 of the surface is blue up to the feet of the spectator. This co- 

 lour gradually diminishes on the right, where the walls of the 

 grotto are most distant from the entrance. The white light al- 

 luded to illuminates the roof sufficiently to shew its natural co- 

 lour ; but when the entrance is obstructed by a boat, or what is 

 better still, when it is wholly covered up by a dark curtain, the 

 roof itself is bluish ; the effect is similar to that produced by the 

 flame of spirits of wine in a dark room : there is then no other 

 light than that which issues from the water. The experiment 

 with the curtain, which is very easily performed, ought to be 

 omitted by none who wish to see the spectacle in all its beauty. 



When a spectator sees from the landing-place a boat pass be- 

 fore him, it causes no reflexion, and throws no shade on the water. 

 If he then put his hand upon his eyes in such a manner that he 

 sees nothing but the water and the boat, the latter will appear 

 suspended in the air, like a black silhouette, traversing the sky. 

 This efi^ect is so striking when seen for the first time, that one 

 cannot avoid experiencing a feeling ^<^f^ uneasiness for the indi- 

 viduals who afford the spectacle. , .,;, 



In the dark place towards the right, whith I have already 

 mentioned, the water is not blue, but is remarkably transpa- 

 rent. The rock under the water is seen by a feeble light, 



• Beyond this landing-place the grotto communicates with a natural gal- 

 lery, about 100 feet in length before it becomes too narrow to admit of pass- 

 ing. From the entrance to this gallery a view of the blue water is obtained 

 across two arcades separated by a pillar ; it is from this point that many ar- 

 tists have taken views of the grotto. 



