along the route. Piston ventilation would make a change of air therein at least six times per hour." However, on page 12 of his report, Mr. Arnold suggests that "4 disk fans should be installed at each station at a cost of not over $5,000. per station."
Examining the different recommendations of Mr. Arnold it is clear that subway construction and operation would practically cease if it were necessary to ventilate them by means of actual mechanical "refrigeration" predicated upon anything known to science today. As to the second recommendation that of "cooling the air" by water spray as was done at the Brooklyn Bridge, enough has already been said to show the futility of this method. The third suggestion, to "keep open the louvres" and cut additional gratings in the sidewalks and elsewhere, is equivalent to throwing away the louvres as useless and resorting to the original suggestion of Engineer Rice to punch more holes in the roof of the subway and let the agitation of the trains take the place of agitation for better ventilation by the people themselves. The fourth suggestion of building within the subway a "division wall" between the uptown and downtown tracks which, to quote Mr. Arnold, "would result in a change of the air in the subway once every 10 minutes," would obviously result only in an enormous additional cost without accomplishing anything whatsoever since, to be effective, the piston would have to be as wide as the two divisions instead of one-half as wide as is the case.
The fifth suggestion made was that "disk fans be installed at every station," but just how this was to change the entire contents of the sub-
Diagram E
