Our large lecture hall used to have a loud horn installed underneath the
floor (accessible from the basement). It could be sounded inconspicuously
by the lecturer. Some of our older professors liked to use it, in mid-
sentence, acting as if they were just as startled as the students.
Unfortunately, the horn is no longer there.
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Laurent Hodges, Professor of Physics lhodges@iastate.edu
12 Physics Hall, Iowa State University, Ames, IA 50011-3160
(515) 294-1185 (office) http://www.public.iastate.edu/~lhodges