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- 



