REPORT ON METEOROLOGY. 
V53 
in the course of a clay as much vitreous electricity as would 
charge a powerful battery. The second source is evaporation. 
The experiments of M. Pouillet went to prove the unexpected 
fact, that the conversion of pure water into vapour excites no 
electric tension. As however this applies only to water and 
other fluids in a state chemically pure, it makes no difference 
in the efficacy of this change as productive of atmospheric 
electricity. It is needless to observe how extensive and pow¬ 
erful must be the result of this action. 
It is hence easy to conceive how the electricity, produced 
by these and other sources, must vary in different climates, sea¬ 
sons and localities, and at different heights in the atmosphere. 
The general principle of the formation of electrical clouds, and 
the production of thunder and lightning, is easily apprehended; 
but the fact of our almost total ignorance of any one step of 
the process cannot be disguised, and, as M. Pouillet frankly 
admits, “il faut avouer si la principe de la formation des nuages 
orageux ne presente pas des difficultes, les applications en pre¬ 
sented, parceque nous n’avons pas assez de donnees sur la 
formation des nuages elle-memes.” 
It is generally believed that in fine weather the electricity of 
the air is positive, and increases in intensity as we ascend. 
Upon these points however observers are by no means agreed, 
and the subject opens a wide field for experiment. From the 
observations of M. Schubler, it would appear that in the climate 
of Europe the electricity of precipitations is more frequently 
negative than positive in the ratio of 155 : 100, but the mean in¬ 
tensity of the positive electricity is greater than that of the 
negative in the ratio of 69 : 43*. 
There is a subject intimately connected with electricity which 
we are unwilling totally to pass over in this place, although little 
has lately been added to our knowledge upon it, because we think 
that it has not excited the attention in this country which it de¬ 
serves ;—we mean the phenomenon of Hail. The difficulty of ac¬ 
counting for the retention of masses of ice in the free atmosphere 
till they attain in some cases the diameter of several inches, is cer¬ 
tainly very great. Perhaps no hypothesis more satisfactory, cer¬ 
tainly none more ingenious, has followed that of Volta, who con¬ 
ceived from the highly electric condition of the atmosphere, almost 
universally attending the production of hail, that the frozen 
masses were kept in a state of reciprocating motion between two 
clouds oppositely charged with electricity, until the increase of 
the mass rendered the force of gravity predominant, or the elec¬ 
tric tension of the clouds was exhausted by mutual reaction. It 
* Bibliotheque Univcrselle, xlii. 203. 
