Extension pieces at the bottom of the shelf supports permit 
two sizes of shelves to be used in the same compartment. The 
librarian may therefore arrange together all books on the 
same subject regardless of size of the volumes. Shelves are 
readily adjustable vertically at intervals of five eighths of 
an inch so that maximum book capacity may be obtained 
together with instant and convenient access to the books.
       Open bar book shelves are used. Light, flexible, and 
strong, they provide support for the books along the full 
length of their lower edges. Further, the shelves present a 
minimum surface for the collection of dust and assist in the 
ventilation and preservation of the books. Under the fixed 
bottom shelves, Z-shaped curbs protect the books on decks 
below from damage and dirt.
       To take care of expansion of various collections of 
books, provision has been made so that auxiliary aisles 
running parallel to the five-foot main aisle may be converted to 
book storage purposes. There are six and a half miles of 
aisles in the bookstack tower.
       Inasmuch as modern students of specialized subjects 
desire access also to books on general or allied subjects, 
books housed together for one department of study are as far 
as possible made accessible to all departments. Two stack 
tiers are equivalent to one building story, and correlation of 
books is thus facilitated, each two tiers of stack serving the 
special departments on the adjacent floors.
       For the serious student, the study carrel or cubicle is 
increasingly popular. The stack floors in the Yale Library 
are equipped with carrel partitions at the windows, forming 
some 330 cubicles four by five feet. They are designed so that 
students studying special subjects may be conveniently located 
with reference to books in the adjacent stack sections. 
Each carrel is equipped with three adjustable shelves and a 
desk with a drawer which may be locked. Here students can 
collect their books and manuscripts and work in peace, with 
volumes required for reference near at hand and available