76 TEACHING SCIENCE IN THE ELEMENTARY SCHOOL

 to children on their own levels of reading ability. Unit
 libraries on about 250 subjects are now available, includ-
 ing such science topics as airplanes, fire, food, light, saf-
 ety, seed dispersal, time, and weather.
 2. Unit picture collections. Unit Picture collections have
 been prepared to accompany a number of the subjects in
 the unit libraries. Each collection consists of from three
 to thirty pictures carefully mounted.
 3. Package libraries. A package library is a collection
 of printed materials dealing with a single subject. It
 contains books, pamphlets, reports, magazine articles,
 and reprints. It contains reference material for older
 pupils and for teachers.
 4. Dramatic materials. Plays for children and adults are
 lent for reading only, not for production materials.
 Some of the materials relate to science, particularly plays
 on health and safety.
 Libraries are lent as requested by any Florida teacher,
and the only charge is postage from Gainesville and return.
For a complete listing of titles and directions for ordering, write
to Miss Bernice Mims, Extension Library Service, General Ex-
tension Division, Gainesville.

Audio-Visual Materials
 The use of audio-visual materials in the classroom holds a
definite place if they are used to:
 1. Develop correct initial concept
 2. Enrich and vitalize instruction
 3. Effect an economy of time in learning
 Accurate representation ranks next in value to the use of
the object, in the forms flat pictures, photographs, models,
museum specimens, film strips, movies, hand made slides, and
different crafts, and recordings. Two types of material, flat
pictures and hand made slides, are of frequent use in the
classroom.
 Flat Pictures. Of all the means of presentation the flat
picture is the most familiar. It is present in newspapers, in
magazines, in advertising and displays, as well as in textbooks.
Visual images are basic to ideas and thinking. There are many
advantages in using flat pictures. They can be used for close
or protracted study, can be used repeatedly with little effort
in handling and with little loss in deterioration. They are eco-
nomical and cover almost every subject.