No Sun-baths through ordinary Window Glass
Many people bask in the warmth of the sunlight as it comes through ordinary window-glass, wrongly thinking they are getting sun-baths. They are getting light and heat baths; but they are not getting sun-baths, for ordinary window-glass will not permit passage of the ultra-violet rays. A room may be flooded with light, or broiling under direct sunlight, as in a solarium or hothouse, yet have none of the life-giving actinic rays. Physicians used to prescribe for patients exposures to the light of the sun through windows, and for a long time the observing ones wondered why those so exposed did not pro¬gress as well as those who were exposed directly to the sunlight in the open air. Even with plenty of fresh air provided, patients will not make much progress under these conditions, nor will sunlight received through ordinary window-glass give immunity to diseases known to be preventable by sunlight. Hence, the discovery of certain methods of treating glass and some other transparent substances so that most of the actinic rays will pass through is one of the most vital and im¬portant that has been made by modern science.