Report of the Progress of the Sciences in France. 25 



derable portion of the substance to be analysed, always resists 

 the affusion of new quantities of acid. 



The best method of producing an almost complete solution 

 consists in using sulphuric acid, and a considerable quantity of 

 potash, which nevertheless ought not to neutralize all the acid. 

 By this means we obtain a salt which has the cliaracters of 

 alum, although it contains a jjroportion of alkali greater than 

 that which is necessary to the crystallization of common alum, 

 and we may dissolve the earth with the exception of the same. 



It results from all the above observations : 



1. That the snow or hail which fell at Arezzo derived its 

 colour from a very fine earthy substance interposed with uni- 

 formity between the small crystals of the hail, without however 

 being inclosed in their nucleus. 



2. That this substance is composed almost entirely of alu- 

 mine, verv little carbonated lime, and a still less quantity of iron, 

 manganese, and silex ; finally, of a very feeble animal or vege- 

 table principle, capable of being carbonized by the action of 

 sulphuric acid and of putrefying water. 



I do not mean to decide upon the etiology of the phaeno- 

 menon >\ hith took place during some grand electrical operations 

 of nature ; but it ought by no means to be ascribed to the 

 stormy nature of the winds. 



In fact, no stornCi was experienced in the town or environs : 

 besides, the wind could not produce effects so perfectly identical 

 to a great extent, or in all directions, nor porjjhyrize the earth, 

 nor divide it with so much regularity in the mass of snow or 

 hail. Lastly, the ground being every where previously covered 

 vvith snow, it can scarcely be supposed that the wind could 

 take up an argillaceous earth with it to scatter it afterwards 

 with fresh snow. 



VIII. Report of the Progress of the Sciences in France in 1813. 

 B}/ J. C. Delametherie. 



[Concluded fVom vol. xliii. p. 439.] 

 PHYSICS. 



X HIS branch of science determines the laws of motion in va- 

 rious bodies, and these are divided into two jiarts ; viz. those 

 which relate to solid bodies, and those which relate to fluid 

 bodies. Lagrange in his Mecaniijiie (tome i.) considers these 

 laws under two different heads. 1. Statics, or the theory of 

 equilibrium. 2. Dynamics, or the theory of motion. The 

 theory of the equilibrium of fluids is consequently denominated 



Hydro- 



