238 KEPORT ON THE TRANSACTIONS OF THE SOCIETY OF 



snow in the summer of 1858 in many localities which he visited, and 

 which, being situated afcove the limit of perpetual snow, are habitually 

 covered with it. M. Marcet, from his own observation, remarked 

 upon the great inequality in the distribution of snow during the 

 winter of 1858, so that while so little had never within the memory 

 of man fallen in the valley of Zermatt, there had, on the contrary, been 

 extraordinary falls of it in the canton of Uri in May of the same year. 



We are indebted to'M. Chaix for several other communications on 

 different points of terrestrial physics and of meteorology. Such are 

 those relative: 1st, to the meteorology of Africa, according to obser- 

 vations given in the travels of Barth; 2d, to the change in the bed 

 of the Yellow river during the last three years, as noticed by Captain 

 Osborne; 3d, to the geographical labors executed by the English, and 

 more particularly by the brothers Gregory, in Australia, from 1842 

 to 1858, in the course of 24 expeditions, which traversed in the whole 

 a distance of 32,000 miles, and which led to the discovery of a great 

 number of salt lakes, often ephemeral, of twelve large rivers subject to 

 the same defect, and of a great number of esculent vegetables, whose 

 existence in that continent was not before suspected. 



M. Henri de Saussure, on his part, has communicated observations 

 which he had made on the distribution of the waters in the basin of 

 Mexico. From these he concludes that the lakes which environ the 

 city of Mexico have heretofore occupied a much larger surface than 

 at present, the retreat of the lakes having been due chiefly to a canal 

 excavated by the ancient Mexicans, and he proclaims the danger of 

 inundation which now threatens the city of Mexico in consequence of 

 the heedlessness of the inhabitants, who have allowed the canal to 

 become completely obstructed. 



We must not forget to mention that our notice has been called by 

 M. Chaix to the levellings made by M. Bourdalone with a view to the 

 opening of the Isthmus of Suez, from which we learn that the differ- 

 ence of level between the two seas is but a few inches. 



General Dufour has likewise communicated the results obtained by 

 M. Bourdalone in his levellings of the course of the Rhone, the descent 

 of which is 39 metres in its passage across the canton of Geneva, ad- 

 mitting that the mean level of the Lake of Geneva is 373 metres above 

 the mean level of the Mediterranean. It is true that previous level- 

 lings gave an altitude of 375 metres above the ocean; but the difference 

 between the two numbers would appear to be owing in great part to 

 the level of the Mediterranean being higher than that of the ocean. 



While speaking of the Rhone and the lake, let us recall the obser- 

 vation of Professor Colladon on the azure color of their waters, which 

 he attributes to particles from the bottom of the lake held in suspen- 

 sion by the agitation of the water. He founds this opinion on a fact 

 observed by himself, viz: that while the dredging machine was at work 

 in winter on one of the shores of the lake, the corresponding arm of the 

 Rhone assumed the deep blue tint which commonly is only seen in 

 summer, at which season a greater quantity of water and stronger 

 current Avould produce the same effect. The cause assigned by M. 

 Colladon may possibly contribute in part to the remarkable phenom- 



