ARRAN. WATER. 333 



stances that attend the cascade. The fall of Scaffhausen 

 has long been celebrated for its green water, but the 

 colour is common to all clear waters under similar cir- 

 cumstances. 



Green is therefore the natural colour of fresh as it is 

 of sea water ; displaying itself whenever the circumstances 

 are the same in both, and only more rarely observed 

 because more rarely free from obstructing impediments. 



I cannot however quit this subject without noticing 

 an hypothesis respecting the cause of the green colour, 

 which seems groundless. It has been said that as the 

 colour of the atmosphere is blue, and as green is not a 

 simple colour, the colour of water must also be blue, and 

 that the green is a result of the mixture of clay or of some 

 yellow tinging substance with its natural blue tint. The 

 first part of the proposition does not appear in any 

 respect to present a legitimate inference ; as it it not 

 at all necessary that because vapour reflects a simple 

 colour, water should not reflect or transmit a compound 

 one ; if it were even certain that green is necessarily 

 compounded of blue and yellow rays. With respect to 

 the latter opinion, there is not the slightest ground for 

 supposing that any yellow substance is held in solution 

 in water, either fresh or salt ; and it is equally impossible 

 that yellow clay should be held in a state of suspension 

 in water, in sufficient quantity to give it colour at the 

 depth of a few feet, or at any depth, without destroying 

 its transparency. It is almost superfluous to add that 

 yellow clay is a rare substance, and assuredly it is not 

 dispersed through the whole mass of the ocean. 



There is an exception to the proposition here main- 

 tained respecting the green colour of water, but it is 

 a solitary one. This is the blue colour of the Rhone 

 as it issues from the lake of Geneva. It has long been 

 known, but has unaccountably remained without even 

 an attempt towards a rational investigation. Even the 

 accompanying circumstances which might afford ground 



