Illustrated and Descriptive Catalogue and Price List of Stereopticons, Lantern Slides, Moving Picture Machines, Accessories for Projection (1902)
W.B. Moore · W.B. Moore: Chicago · leaf 20
ox containing buzzer and batteries is placed at the machine with the operator. Sound of buzzer can be so regulated as to be heard only by the operator, and ' will therefore not interrupt the lecturer by attracting the attention of the audience. Electric Signal No. i has 75 feet of flexible covered… … No. 1 or No. 2 is wanted. ELECTRIC SIGNAL NO. 2.
