Since the discovery of electricity man has speculated on the effect of the electrical condition of the atmosphere on his health and comfort. The oppressiveness that people feel before a storm, the exhilaration experienced after it has passed, the feeling of the freshness of mountain air and, conversely, the ill effects of hot, dry wind were considered to be related to the state of electrical charges or ions in the air.

Stuffiness indoors was also thought to be due, in part, to the ion content of the air.

Over the past fifty years interest in artificially altering the ion content of air for clinical treatment and human comfort has been surrounded by controversy, mainly because of the conflicting results obtained from various studies of the effects of air ions on comfort and health.

Although the use of ion generators in heating and ventilating systems is not common at present, a resurgence of interest occurs from time to time.

The nezt several articles will review, very briefly, the current state of knowledge of air ions, both naturally and artificially produced, with particular attention to their possible effect on human comfort and health.