322 SALMONIA. 



dissolved in minute portions in water, and 

 this, mixed with the blue of pure water, 

 would occasion sea green. I made, many 

 years ago, being on the Mer de Glace, an 

 experiment on this subject. I threw a small 

 quantity of iodine, a substance then recently 

 discovered, into one of those deep blue 

 basins of water which are so frequent on 

 that glacier, and, diffusing it as it dissolved 

 with a stick, I saw the water change first to 

 sea^ green in colour, then to grass green, and 

 lastly to yellowish green : I do not, however, 

 give this as a proof, but only as a fact fa- 

 vourable to my conjecture. 



PoiET. — It appears to me to confirm 

 your view of the subject, that snow and ice, 

 which are merely pure crystallized water, 

 are always blue, when seen by transmitted 

 light. I have often admired the deep azure 

 in crevices in masses of snow in severe win- 

 ters, and the same colour in the glaciers of 

 Switzerland, particularly at the arch where 

 the Arve issues, in the Valley of Chamouni. 

 We thank you for your illustration. 



Hal. — In return, I ask you or some ur- 



