800 Intelligence and Miscellaneous Articles. 



air from various natural sources ; recompositions of the two electri- 

 cities must therefore continually take place. The result is an excess 

 of positive electricity when the sky is serene ; for this purpose it is 

 necessary that the sources which furnish this electricity should be 

 the most numerous, and these sources are probably vegetation and 

 the contact of soils and waters. 



After recalling all that we know of the formation of storm-clouds, 

 I have pointed out that the storm does not generally burst except 

 when two clouds charged with opposite electricity are in presence 

 of each other, or when a strongly electrified cloud comes within 

 the sphere of the earth's activity. In these two cases there is action 

 b}' influence and a re-establishment of equilibrium. Thus in places 

 where sources of opposite electricity exist at some distance apart, 

 these localities combine the principal conditions for the production 

 of storms. 



In the polar regions the rarity of storms is probably connected as 

 much with the absence of evaporation as with the small number of 

 natural sources of electricity ; just as under the tropics the fre- 

 quency of storms is in relation to the abundance of evaporation and 

 that of the sources of electricity. 



The diminution of storms in advancing, on the one hand, into the 

 continents, and, on the other hand, in departing from the coast into 

 the open sea, where it very rarely thunders, seems to indicate that 

 the greatest number of sources of opposite electricity exist at but a 

 small distance from the coasts ; it is there consequently that they 

 must be sought. 



Fifth Part. On the Crystalline Compounds formed in slow actions 

 with or without the concurrence of electrical forces. — The examination 

 of the natural sources of electricity which must intervene in the 

 phaenomena of decomposition and recomposition of mi ueral substances, 

 has led me again to the study of the slow actions which take place 

 with or without the apparent concourse of electricity, a question 

 which possesses a high degree of interest for geologists. In the first 

 place, I have indicated the improvements which 1 have introduced 

 in the processes which I have hitherto made use of to obtain various 

 metallic oxides, and double or simple basic salts in a crystalline form ; 

 I have then shown how the following products may be obtained cry- 

 stallized in the space of several years, upon mineral substances placed 

 in suitable conditions : — 



1 . The double carbonate of lead and soda upon galena in small 

 acicular crystals, which will be found some day in lead mines into 

 which water charged with bicarbonate of soda filters ; 



2. Carbonate and sulphate of lead upon galena in crystals similar 

 to the native ones ; 



3. Arseniate of lime upon sulphate of the same base, exactly 

 similar to what is met with in some veins ; 



4. Bibasic phosphate of lime crystallized, with phosphate of cop- 

 per upon limestone ; 



5. Double combinations, which will be found described in ray- 

 memoir ; 



