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 \\ e 

 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, 



