Scientific InteUignce. — Hydrology. 427 



evaporation may have some effect upon the phenomena, M. 

 Belli ascribes the principal influence to the action which atmo- 

 spheric electricity must exercise upon running water. Water, 

 he says, will be by influence, by induction, in a state of nega- 

 tive electricity, when the atmosphere is, as usually happens, 

 charged with positive electricity. At the moment in which 

 this water is divided into a thousand globules, it cannot fail to 

 convey the electricity, with which the impulsion of the atmo- 

 sphere had impregnated it, to every object which it encounters. 

 The theory of Professor Belli is susceptible of a proof which, 

 at once, will demonstrate either its truth or its inaccuracy. If 

 it be true, the electricity of the vapour with which waterfalls 

 are surrounded, will not be always of the same kind ; it will be 

 negative if the atmosphere is positive; and, on the contrary, it 

 will be found positive when the clouds are negative. It must, 

 then, be observations made in the time of storms, and not under 

 a serene sky, which will enable us to ascertain the comparative 

 merits of the theories of Volta and M. Belli. — Arago. 



11. Tides in the Mediterranean. — The theory of tides, bor- 

 rowed from the principle of universal attraction, can leave no 

 doubt as to its general truth. What it still wants in sim- 

 plicity and accuracy will be afforded by geometry. Observers, 

 at the same time, have a great field of inquiry before them, 

 in the local circumstances which considerably modify the tide- 

 tables of different ports, and the changes in the height of the 

 water, where it is not easy to state what is the influencing cir- 

 cumstance, and what its mode of action. Are there any sensi- 

 ble tides in the Mediterranean properly so called.'^ To this 

 question some individuals respond yes ; as it concerns, for ex- 

 ample, the harbour of Bouc ; but the calculations on which 

 they rest give a contrary result. According to some researches 

 made at Naples, in the year 1793, there was there a very ob- 

 servable tide to the extent c)f about a foot in the straight canal 

 which is called the river Styx^ and which establishes a com- 

 munication between the port of Mistne and the Mare-Morio. 

 Blagden regarded these data so certain that he even proceeded 

 to deduce from them the hour of its establishment in the Bay 

 of Naples. These observations deserve to be repeated in differ- 

 ent parts of the coast of Algiers ; and the want of success in 

 some harbours ought not to prove discouraging as it regards 



