540 POPULAR SCIENCE MONTHLY. 



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 chiefl}^ 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 



Sunset over a Sea of Fog. 



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 

 tlie potential values. There was also good reason for believing that 

 the electrometer gave in certain fluctuations indications of the prox- 

 imity of invisible vapor masses. Certainly the one instrument upon 

 which we now rely in studies of fog formation and influence, the mer- 

 curial thermometer, is far from being a sufficiently sensitive instrument. 

 Optical methods may furnish apparatus sufficiently delicate. It has 



