On the Colour of the Attnosphere and Deep Water. 355 



epaque particles produce the same effect in the glacier as the 

 white plate and the bottom of the sea. 



On the shore of the island of Capri, there is a grotto which 

 Nature seems to have constructed to shew the blue colour of 

 the sea in all its beauty, and which, for that reason, bears the 

 name oi grotte d'azur ; it i? situate under a rock, on the north 

 side pf the island. As it cannot be entered by a boat of ordi- 

 nary dimensions, it remained unknown till the month of August 

 1826, when two Prussian artists, MM, Kopitch and Frisi, swam 

 into it, and examined it. Their description having excited the 

 curiosity of the public, boats of suitable dimensions were con- 

 structed, for conveying amateurs into the interior. 



The entrance to the grotto is four feet five inches English in 

 height, and about the same width, nearly in the shape of an 

 equilateral triangle, one of the sides of which is formed by the 

 sea. The summit is rounded, and by no means wide, so that 

 it is passed by a slight inclination of the head, when we enter 

 into a spacious grotto, the roof of which is remarkably regular, 

 as well as the wall which supports it. Its extent, measured from 

 the entrance to the landing-place opposite, is 125 English feet 

 in the direction from north to so^uih, while it is 145 feet from 

 east to west. The depth of the water under the entrance is 67 

 feet, in the middle of the grotto it is 62^ and near the landing- 

 place 58 feet^33^3^ yhoik^s^ ^ ylno bfro id: . 



The rock is calcareous, of a light grey colour in the fracture, 

 and there is no appearance of stratification. 



On entering all appears pbscure, except the water, which is 

 bright and of a brilliant blue, contrasted with the general ob- 

 scurity. Our constant experience of seeing the light come from 

 the sky, is no doubt one of the causes of surprise produced by 

 this pacu'liar blue light issuing from the depths of the sea. 

 Advancing towards the end of the cave, while the boat is still 

 in the direction of the entrance, the end of the white oars shines 

 in the water with a bright blue light, which disappears as soon 

 as they are raised. This is the most remarkable phenomenon 

 which the azure grotto presents; for it is not easy to understand 

 ^hy objects are fio brightly illuminated in the water, and no 

 longer so immediately above tlie surface. When the hand or a 

 cloth is plunged into the water, one would believe that it was 



