Page:Popular Science Monthly Volume 59.djvu/550

540 removal of the fog for even a small distance in the neighborhood of a fog-bound vessel might be of advantage. The chief difficulty at present would seem to be the quick influx of the circumjacent fog. The supply of fog might be so great that our dissipators would seemingly produce no effect. The dissipation of fog and smoke in enclosed areas by electrical agencies, as strikingly shown in Dr. Lodge's experiments, leads to the wish to reproduce these experiments in the free air and upon a large scale. Moreover within the past two years there has been growing up a theory due chiefly to Zeleny, Elster, Geitel and T. C. K. Wilson concerning the part played by ions in causing rain. It is known that the negative ions move more rapidly than the positive ions and that water vapor will condense more readily on the negative ions. It may

be that under certain unstable conditions some of the more energetic ions, by relieving the electric tension, inaugurate the formation of the rain-drop. In studying the electrical potential of the atmosphere, it has been shown that the approach or retrocession of clouds, especially cumulus and cumulo-nimbus, could be determined by the changes in the potential values. There was also good reason for believing that the electrometer gave in certain fluctuations indications of the proximity of invisible vapor masses. Certainly the one instrument upon which we now rely in studies of fog formation and influence, the mercurial thermometer, is far from being a sufficiently sensitive instrument. Optical methods may furnish apparatus sufficiently delicate. It has