ABOUT COMMON WATER. 843 



Blue is the natural colour of both water and ice. 

 On the glaciers of Switzerland are found deep shafts 

 and lakes of beautifully blue water. The most striking 

 example of the colour of water is probably that furnished 

 by the Blue Grotto of Capri, in the Bay of Naples. 

 Capri is one of the islands of the Bay. At the bottom 

 of one of its sea-cliffs there is a small arch, barely 

 sufficient to admit a boat in fine weather, and through 

 this arch you pass into a spacious cavern, the walls and 

 water of which shimmer forth a magical blue light. 

 This light has caught its colour from the water through 

 which it has passed. The entrance, as just stated, is 

 very small ; so that the illumination of the cave is 

 almost entirely due to light which has plunged to the 

 bottom of the sea, and returned thence to the cave. 

 Hence the exquisite azure. The white body of a diver 

 who plunges into the water for the amusement of 

 visitors is also strikingly affected by the coloured 

 liquid through which he moves. 



Water yields so freely to the hand that you might 

 suppose it to be- easily squeezed into a smaller space. 

 That this is not the case was proved more than two 

 hundred and sixty years ago by Lord Bacon. He filled 

 a hollow globe of lead with the liquid, and, soldering up 

 the aperture, tried to flatten the globe by the blows of 

 a heavy hammer. He continued hammering ' till the 

 water, impatient of further pressure, exuded through 

 the solid lead like a fine dew.' Water was thus proved 

 to offer an immense resistance to compression. Nearly 

 fifty years afterwards, a similar experiment, with the 

 same result, was made by the members of the Academy 

 Del Cimento in Florence. They, however, used a globe 

 of silver instead of a globe of lead. This experiment is 

 everywhere known as * the Florentine experiment ' ; 



