WATER AND ELECTRICAL STORMS.
In early days water and water vapor—evaporation and condensation—were presumed to be important factors in the origin of atmospheric electricity. Volta thought that rising water vapor is negatively charged, the water from which it arises being positively charged; and Peltier believed that aqueous vapor carries up with it part of the electric charge of the earth. But there is no proof that the evaporation of water is accompanied by a separation of the two electricities, nor has it been established that the vapor from electrically charged water carries any charge with it. There is a great deal of experimental evidence, but it is not by any means in complete harmony. Bartoli could find no sign of electrification due to mere evaporation; and Pettinelli has continued this work with organic compounds,—alcohols. aldehydes, etc.,—with the same negative result. Lord Kelvin, Magnus MacLean. and Alexander Gall observed that a carefully dried air current charges pumice stone soaked in sulphuric acid positively, esoeciallv when the air has to bubble through the acid; but no change was observed when the pumice stone was moistened with water. They further found that air bubbling through pure water becomes negatively electrified, while with salt water it becomes positively electrified. If the air is previously electrified, however, a positive charge is diminished by pure water and a negative charge by salt water; and the charges arc increased, if the original charges arc opposite to those here supposed. But such charges, and, further, the charges imparted to air which is blown through a metallic case with a metallic point in the centre, the case and point forming electrodes connected with an induction machine, disappear, if the air is filtered through a sufficient number of wiregauze screens or cotton batten plugs. These observations, which were not all concordant, and the experiments with air currents passing through hot tubes, suggest that dust particles of various descriptions, and friction, play a part. Holmgren states that a fine current of air emerging from water is positively charged to seventy volts, and that concussions and friction between solids and water generate electricity. According to Lenard, confirmed by Wesendonck and others, waterfalls that dissolve in drops and mist make the air negative; while solids and liquids, against which the air streams make it positive, the water itself appearing to be unelectrified. This is when the water is pure; for salt water sprays give rise to positive electrification. The presence of dust facilitates the condensation of water vapor; but it has been doubted if condensation is possible without nuclei of some sort—dust particles or their equivalents—the term “dust” being taken in a very wide sense. The researches of C. T. R. Wilson show that expansion suffices to bring about condensation in air that is saturated with aqueous vapor. Nuclei having a diameter of 0.000,000,025 of an inch are sufficient to produce cloud-like condensation, and these are always present in all gases containing water vapor. Rain-like condensation is produced only when somewhat larger nuclei are present. The influence of a slight electrification by induction on the nature of drops has long been known. A high vertical water jet soon breaks into drops, which are scattered in all directions; but, when a piece of rubbed scaling wax is held near, the jet flows quietly and the drops coalesce. With a strong electrification, the scattering is worse than without any. W. von Bczold, in com mon with many others, believes that strong ascending currents of air prevail in both kinds of storms, these currents preventing the large masses of water assembled in clouds from sinking until the unstable equilibrium breaks down, owing to local conditions (beat-storms) or to changes initiated at a distance (whirl storms). The causes for the breakdown are the lower strata, the cooling of the higher ones, supersaturation with aqueous vapor, the overcooling of water drops, and changes in the state of aggrega tion.