He telegraphed to Mummy to come up to London and bring him up his epidiascope and slides, and he rigged it all up in the ship and started giving lectures to the crew.    From Wordnik.com.  [The Breaking Wave]

Not that long ago, a classroom-style overhead projector (properly called an epidiascope) with A4 transparencies and a marker pen was the norm for most conferences.    From Wordnik.com.  [Brad Ideas - Comments] Reference