fundamental requirements. First, books and their preservation; 
second, the occupants of the building, both employees 
and students, and their comfort; third, equipment simple 
and durable and, at the same time, as inexpensive to operate 
as possible.
       In designing the equipment climatic conditions had to 
be considered, and known data regarding the preservation 
of books and comfort of occupants had to be kept in mind. 
The climatic conditions in New Haven are approximately 
as follows. During the heating season the average outdoor 
temperature is about 38° F. with a known low of -16° F., 
but with a low temperature of 0°F. possible several times in 
a season, The relative humidity out of doors is reasonably 
high, but naturally outside air has a low relative humidity 
after being heated to a comfortable room temperature. During 
the non-heating season the average temperature is about 
75°F., but during the summer months temperatures of from 
85° F. to 90°F., accompanied by relative humidities of 60
per cent to 65 per cent are not unusual, and in recent years 
there have been 8 A.M. records of about 75° F. temperature 
and 90 per cent relative humidity. In addition to the above 
conditions there appears to be a more or less definite opinion 
among engineers and others interested in libraries that air 
conditions which are good for normal human beings are 
about right for the preservation of books. The present 
recommendations are 68° F. dry bulb temperature and 40 per cent 
relative humidity, both kept as uniform as possible.
       The heating and ventilating system installed is the so-called 
split system, that is, sufficient direct radiation is installed 
to keep the temperature in the building at 70° F. and 
the air for ventilating is delivered at room temperature.
       Using the above data as a basis, the stack space was 
provided with ducts, fans, filters, and humidifiers to deliver 
100,000 cubic feet of air per minute to the stack space. This 
amounts to approximately three changes per hour. This air 
is delivered by three fans, one for the lower third of the stack