The pump organ is a type of free-reed organ that generates sound as air flows past a vibrating piece of thin metal in a frame. The piece of metal is called a reed. Specific types of pump organ include the reed organ, harmonium, and melodeon.
The Hammond Organ on '120 Years Of Electronic Music' – includes original patent diagrams for the instrument; Media "Electric Pipeless Organ Has Millions of Tones". Popular Mechanics. No. April 1936. Hearst Magazines. April 1936. pp. 569–571. One of the first large, detailed articles on the Hammond Organ and how it worked