300 ILLINOIS ACADEMY OF SCIENCE 
6. The records of the Weather Bureau show that the av- 
erage temperature for January, for eastern Iowa, southern 
Wisconsin, the Lower Michigan Peninsula, Northern Illinois, 
Indiana, Ohio, Pennsylvania, New York, New Jersey, and 
most of New England is from 20° to 30°, while the average 
relative humidity of this region for January is from 75 per 
cent to 85 per cent. (Figs. 3 and 4). In this region live 
nearly one-half of the population of the United States and 
here is found more than one-half of the wealth and resources 
of the nation. If the control of indoor climate during the 
winter months is as important for human health and vitality 
as recent writers assert, we certainly need more information 
concerning the methods by which it may be obtained. 
An outdoor temperature of 25° with a relative humidity of 
80 per cent means an absolute humidity of 1.241 grains of 
moisture per cubic foot. If this air is admitted to the residence, 
school or counting room heated to 70° without the addition 
of moisture, a relative humidity of 15.5 per cent results. This 
is a much lower relative humidity than is to be found in out- 
door air in any inhabitable region on the face of the earth. 
The effect of frequently passing from indoor air at a tem- 
perature of 70° and a humidity of 20 per cent or lower into 
outdoor air at 25° and 80 per cent humidity is a matter which 
aoe) 
should receive more attention. 
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Fig. 4. Average Relative Humidity for January for 15 years. 
