TIDES, WAVES 101 



devised by Paul Regnard. Animals which are 

 quickly brought under pressure with the aid 

 of this apparatus are seen to become inert 

 and apparently dead ; then if the pressure is 

 gradually diminished the animals gradually 

 recover their normal functions and powers of 

 movement, when the intercellular fluids of 

 their bodies have had time to get into equilib- 

 rium with the pressure of the compressing 

 medium. When the sudden increase of 

 pressure exceeds a certain limit, death results 

 through the rupture of the cells of the tissues, 

 which are soaked with water. 



Colour of Sea-Water. — W. Spring made many 

 experiments on the colour of fresh water, and 

 found that ordinary distilled water was of a 

 greenish colour, which he believed to be due 

 to impurities remaining in the water after 

 distillation ; samples of water rendered abso- 

 lutely pure had a beautiful clear blue colour. 

 In the open ocean the water is generally of a 

 bluish colour, and near land and in estuaries 

 green or yellowish green ; within the thirtieth 

 parallels north and south of the equator the 

 colour is a brilliant ultramarine, and to the 

 south of lat. 30° S. it changes rapidly to a deep 

 indigo, which continues as far as the Antarctic 

 Circle, where it changes to olive-green. The 

 blue colour is attributed to the rays of light 

 being unequally absorbed by water, blue rays 



