NINTH DAY.] COLOUR OF WATER. 273 



of this large lake coloured; but; notwithstanding 

 this, the river came from the lower part of it per- 

 fectly clear, and I caught fish in it there with a 

 fly, which at its entrance into the lake was quite 

 impossible. 



POIET. You, Halieus, must certainly have con- 

 sidered the causes which produce the colours of waters. 

 The streams of our own island are of a very different 

 colour from these mountain rivers, and why should 

 the same element or substance assume such a variety 

 of tints ? 



HAL. I certainly have often thought upon the 

 subject, and I have made some observations and one 

 experiment in relation to it. I will give you my 

 opinions with pleasure, and, as far as I know, they 

 have not been brought forward in any of the works 

 on the properties of water, or on its consideration as 

 a chemical element. The purest water with which we 

 are acquainted is undoubtedly that which falls from 

 the atmosphere. Having touched air alone, it can 

 contain nothing but what it gains from the atmo- 

 sphere, and it is distilled without the chance of those 

 impurities, which may exist in the vessels used in an 

 artificial operation. We cannot well examine the 

 water precipitated from the atmosphere, as rain, with- 

 out collecting it in vessels, and all artificial contact 

 gives more or less of contamination ; but in snow, 



T 



