68 TEACHING SCIENCE IN SECONDARY SCHOOLS

 4. The attitude of "going to a movie" is avoided.
 5. Crowding two or more classes together is prevented.
 6. Using assorted films just to fill an hour is less likely.
 (This misuse sometimes develops in an effort to keep
 classes from passing through the hall at times when other
 classes are at study.)
 If at first the classroom showing is not feasible, plan with the
whole faculty to establish this more effective use of films as soon
as practicable.
 Audio Aids. Strictly auditory devices have advantages and
disadvantages all their own. Advantages are that they do not
require darkening a room, with attendant problems of ventila-
tion; they resemble the accustomed classroom method, and they
do not require special projection rooms or seating. If the stu-
dents can hear clearly the teacher speaking, they can hear a
radio or record-player.
 Of the audio aids, radio is the simplest to put into use, but
the most difficult to plan. Many educational broadcasts do not
occur at the scheduled class time. Others are of an unexpected
nature and may, or may not, be given advance publicity. These
factors limit the classroom use of the ordinary radio. For either
direct class use of radio, or delayed use following recording, ad-
vance publicity sent out by the networks and local radio stations
may be obtained. Teacher requests will help create an increased
supply of these broadcast guides.
 With a dual-speed reproducer the science teacher may use
any past events which have been recorded or transcribed. Voices
of famous scientists are available on educational records, as well
as speeches and dramatic episodes. Hearing a voice seems more
personal than looking at a picture. The voices of Edison, Mar-
coni, and Einstein make them more real to students. Many of
the regular broadcasts of the series "Cavalcade of America" and
"Exploring the Unknown" have been recorded and may be bor-
rowed from the Extension Division of the University of Florida
or from the U. S. Office of Education. Others are for sale by
numerous educational recording companies. The National
Broadcasting Company is one of the networks having files of