216 M. Marsollier's Description of the 



probably reunited in two binary combinations having a com- 

 mon element. But it is these binary combinations, the im- 

 mediate elements of the combinations in question, that ought 

 to be compared with one another. 



This seems to show very clearly, that the refraction de- 

 pends not on the mass of the molecules, like specific heat, but 

 on the electric state which belongs to them. 



In reasoning on the hypothesis of emission, the sum of the 

 attractions of the molecules of an elastic fluid on light ought 

 to be independent of the form of these molecules, since these 

 are liable, as in crystallized bodies, to present certain faces in a 

 determinate direction. But if the refraction depended on 

 these attractions, we cannot conceive how the action of a bi- 

 nary compound should be sometimes greater and sometimes 

 less than the sum of that of its elementary molecules. We 

 may, therefore, regard this fact as a new difficulty attached to 

 the hypothesis of Newton. 



Art. V .-—Description of the Grotto of Ganges.* By M. Mak- 



sollier. 



W hen we set out to visit the subterraneous grotto, we expe- 

 rienced at first nothing but fatigue. It was necessary to 

 climb for nearly three quarters of an hour. The sun, the 

 reflection from the rocks, the footpath traced only by the 

 tread of the goats, the rolling stones, the torches, the cords, 

 the provisions of which each carries his part, — all this adds 

 to the difficulty of the expedition. 



On the summit of a rock in the middle of the mountain 

 there rises a small wood of green oak, which affords an agree- 

 able shade, and protects, with its mysterious shadow, the 

 mouth of the cavern. This opening has the form of a cask, 

 the top being about 20 feet in diameter, and its depth about 

 30 feet. This hollow is finely fringed with trees, plants, and 

 wild vines with their grapes, and excites the regret that we are 



* Translated from Marsollier, as given in Renaud de Vilback's Voyage 

 dans k Languedoc, Paris, 1825. 



