504 Prof. E. Edlund on the Magnitude of 



forced to follow the water, since this is the sole medium of 

 conduction. The passage from vapour to liquid water con- 

 sequently produces an enormous condensation of the electricity 

 contained in the water. 



We may remark, further, that the electricity is not distributed 

 in a uniform manner in the liquefied water, but that it is con- 

 tained upon the surface of the drops formed, whence it follows 

 that its density may become much greater than the figures 

 given by way of example. The greater the number of drops 

 formed in the liquefaction of the vapour, the greater is also 

 the sum of the surfaces of these drops. When, further, a 

 great number of small drops unite to form a small number 

 of large drops, this change produces a condensation of the 

 electricity which they contain, the total surface of the drops 

 being diminished by the union. If, now, the air saturated 

 with moisture is considerably extended, and a small quantity 

 condenses only slowly at a certain point, the electricity which 

 condenses there is conducted without producing sensible sparks 

 to other parts of the saturated layer. When, on the contrary, 

 the saturated mass is divided from other masses of like nature 

 by layers of drier air, and a rapid liquefaction of the vapour of 

 water takes place, the high electric tension resulting from the 

 liquefaction cannot be maintained, and the electricity passes 

 by disruptive discharge to the neighbouring clouds, or to the 

 earth when the tension is less. Hence, according to this view, 

 intense and violent liquefaction of the aqueous vapour of the atm o- 

 sphere is the principal cause of the enormous electric tension 

 occurring in the disruptive discharges of thunder-storms. In 

 most cases this liquefaction is accompanied by a violent fall 

 of rain or hail ; but we may nevertheless suppose that under 

 certain conditions the condensation induces only the formation 

 of clouds, accompanied by electric discharges without the fall 

 of water. The liquefaction of the vapour of water does not 

 increase in any way the quantity of electricity existing in the 

 air, but increases its tension in a high degree*. 



* Kantz has already admitted that the liquefaction of the vapour of 

 water is necessary to the production of thunder-storms; he attributed the 

 production of electricity principally to evaporation taking place upon the 

 earth's surface, as well as to the processes of vegetation and combustion 

 (vide Kantz, Lehrbuch der Meteor oloyie, p. 468, Halle, 1832 ; and 

 Vorlesmujen iiber Meteor ologie, pp. 396 and 427, HalJe, 1840). At 

 this time the impossibility of the atmospheric electricity originating 

 under these circumstances had not been demonstrated. Sir John Herschel, 

 following Kantz, assumed evaporation as the principal cause of the elec- 

 tricity of the air. He saw also in the condensation of aqueous vapour 

 the cause of the high electric tension in times of storms. Compare Her- 

 schel's 'Meteorology ' (Edinburgh, 1862), p. 122. 



