612 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1911. 
us all. Contrast your feelings and your effectiveness on a close, hot, 
muggy day in August and on a cool, brisk, bright October morning. 
Many a factory operative is kept at the August level by an August 
atmosphere all through the winter months. He works listlessly, he 
halt accomplishes his task, he breaks and wastes the property and 
the material entrusted to his care. , If he works by the day the loss 
to the employer is direct; if he works by the piece the burden of 
interest on extra machinery has just as truly to be borne. At the 
close of the day the operative passes from an overcrowded, over- 
heated workroom into the chill night air. His vitality lowered by the 
atmosphere in which he has lived, he falls a pray to minor illness, cold 
and erip, and the disturbing effect of absences is added to inefficiency. 
Back of it all lurks tuberculosis, the great social and industrial dis- 
ease which lays its heavy death tax upon the whole community after 
the industry has borne its more direct penalty of subnormal vitality 
and actual illness. 
The remedy for all this is not simply ventilation in the ordinary 
sense in which we have come to understand the term. Mr. R. W. 
Gilbert, of the Massachusetts Institute of Technology, begins a sug- 
gestive paper on ‘‘The econofnics of factory ventilation,” in the Engi- 
neering Magazine for December last, as follows: 
Webster’s definition of the word ventilation is ‘‘to air” or ‘‘to replace foul air by 
fresh.’? In actual practice, however, ventilation should mean more than this. 
It should mean the conditioning of the air of any inclosed space to the best require- 
ments of the occupants of that space. 
Conditioning of the air so that the human machine may work 
under the most favorable conditions—this is one of the chief elements 
of industrial efficiency, as it is of individual health and happiness. 
The chief factors in air conditioning for the living machine, the 
factors which in most cases far outweigh all others put together, are 
the temperature and humidity of the air. In many a plant after 
spending money for an elaborate system of ventilation, the air has 
been kept too hot or too dry or too moist, and the effect on comfort 
and efficiency has been worse than nil. It is a curious instance of the 
way in which we neglect the obvious practical things and attend to 
remote and theoretical ones, that for years more attention has been 
bestowed on the testing of air for carbon dioxide, which was supposed 
to indicate some mysterious danger, than on the actual concrete effect 
of overheating. Yet heat, and particularly heat combined with 
excessive humidity, is the one condition in air that has been proved 
beyond a doubt to be universally a cause of discomfort, inefficiency, 
‘and disease. Flitigge and his pupils in Germany and Haldane in 
England! have shown that when the temperature rises to 80° with 
moderate humidity or much above 70° with high humidity, depres- 
1 The literature on this subject is well summarized with references to original sources by T. R. Crowder 
in “ A study of the ventilation of sleeping cars,’’ Archives of Internal Medicine, vol. 7, p. 85. 
