weather it is practically 100 per cent.[1] During summer rainstorms it is approximately 95 per cent.
The relative humidity of the air has a profound effect upon public health. General Greely noted the fact that, during prolonged spells of very dry air when the per cent of humidity fell materially below the normal, a notable increase in the death rate followed. Dr. Ellsworth Huntington has shown that the same result is true of the death rate in hospitals.
Humanity, both the conscious and the sub-conscious self, is sensitive to changes in temperature, noting a difference even of 1 degree Fahrenheit. The conscious self rarely notices changes in humidity between 35 per cent and 85 per cent. The subconscious self is far more sensitive; it rebels against a condition of humidity materially higher than 75 per cent or lower than 40 per cent when the temperature of the air is that of comfort. There is a noticeable difference to the feelings between indoor and out-of-door air. Indoors, a humidity of 25 per cent is extremely uncomfortable; out of doors it is hardly perceptible.
During the winter season when buildings are artificially heated, the humidity of living-rooms is not often above 40 per cent; usually it is lower than 35 per cent; in school rooms it may be less than 25 per cent. Dr. C.-E. A. Winslow has pointed out the effect upon the health of the pupils of air so deficient in moisture.[2] P. R. Jameson, using empiric but very practical standards of measurement—that is, comfort or discomfort—has tabulated the results of several thousand tests:
| Rel. Hum. 75% | 55° F | very cold | |
| 65° F | chilly | ||
| 75° F | comfortable | ||
| Rel. Hum. 50% | 35° F | very cold | |
| 50° F | chilly | ||
| 65° F | comfortable | ||
| Rel. Hum. 30% | 55° F | very cold | |
| 65° F | chilly | ||
| 75° F | comfortable |
