650 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1907. 
sisted of five cars, and ran at a rate, exclusive of stops, of about 21 
miles per hour. The express trains generally consisted of eight cars, 
and ran at a rate, exclusive of stops, of about 26 miles per hour. 
The total number of passengers carried in the subway, as indicated 
by an official statement of the ticket sales, averaged, for the last two 
months of 1905, 440,000 per day. There were about twice as many 
passengers carried in November and December as in July. 
As a train moved through the subway, air was forced ahead of it 
and air followed it. As a rule, a general current flowed along the 
track on each side of the subway in the direction of the train move- 
ment, and these currents continued even when no train was within 
hearing distance. The important action of a train was to put large 
2s i aa ee a ee ES 
~ ath 
5 a Yo ER | ee 
=| Fan ats CRS] Cee Se (PRE Fe a Ll 
35 Co OB Bee Same ee ere ee) 
Fig. 1.—Rapid variation in temperature noted, with a ventilated thermometer and 
accompanying train movement. The small arrows show the movement of local, the 
large of express, trains in each direction. The changes in temperature were due to air 
currents set up by trains. 
volumes of the air in motion. Where stairways or blowholes oc- 
curred and offered lines of diminished resistance, the air rushed out 
through them as a train approached and rushed in as the train 
went by. 
The difference in barometric pressure necessary to set up these air 
currents was exceedingly slight; the effect of friction against the walls 
and pillars of the subway and the sides of the stairways considerable. 
A great part of the force with which the air currents were set in mo- 
tion was generally used up in eddies about the trains. The rest was 
useful for ventilation. 
The movement of the air depended upon the speed of the nearest 
train, the movement of other trains in the vicinity, the size and loca- 
tion of the neighboring openings to the outside air, the size of the par- 
