AIR OF NEW YORK SUBWAY—SOPER. 651 
ticular cross section of the subway with reference to the sections of the 
moving trains, the force and direction of the wind in the streets with 
reference to the position of the stairways, the difference in tempera- 
ture inside and outside of the subway, and other conditions. 
The chemical analyses of air which were made gave data from 
which the frequency with which the air was renewed could have been 
computed had the number of passengers present at any corresponding 
time and part of the subway been known. Accurate information on 
this subject was not, however, obtainable from the Rapid Transit 
Commission or the operating company. 
Observations with anemometers were made at a number of stations 
on several occasions. As a result of seventy-nine of these observa- 
tions, covering, in the aggregate, two hours and thirty-five minutes, 
made at eight stations, it was calculated that an average of 573,000 
cubic feet of air had moved in and out of one stairway per hour. 
This was at the rate of 9,500 cubic feet per minute. 
The maximum movement of air observed was when 63,000 cubic 
feet passed in at one station in one minute through a single stairway. 
The velocity of the current on this occasion was 164 miles per hour. 
That the air circulated freely from one station to another was 
shown by CO, analyses (to be referred to later) and by noting the 
time that it took an odor to pass from one station to another. Cologne 
of a highly concentrated grade, and in sufficient quantity to produce 
a distinct perfume throughout the air of a station, was used at 
several points and the odor noted up and down the line with the 
help of investigators with stop watches. Care was used that the 
cologne should not be transported mechanically by coming in contact 
with the trains in liquid form. 
As a result of eight cologne experiments, it was found that the 
odor was carried from station to station at the average rate of 271 
feet per minute, or about 3.08 miles per hour. 
The ventilation of the subway bears an interesting resemblance 
to the ventilation of the human lungs, and it will help to understand 
the former if we trace some of the details of this analogy. 
The ventilation of both the subway and the lungs is due to currents 
of air passing inward and outward as a result of changes of pressure, 
caused chiefly by the expansion and contraction of the enclosed space. 
It is true that with the lungs the size of the enclosed space is alter- 
nately enlarged and reduced through the movement of its walls, while 
in the subway the size of the enclosure is increased and diminished 
through what is termed the piston action of the trains; but in other 
respects the similarity is close. 
In the normal amount of air which passes out of the subway on the 
approach of a local train, and is replaced by an indraught of fresh air 
as the train draws away, we have what physiologists, in speaking of 
