https://en.wikipedia.org/wiki/DeLaval
Published
Lantern slides used for teaching agriculture at Belleville Collegiate Institute and Vocational School, Belleville, Ontario, in the 1920s.
These slides were distributed by Scott & Van Altena of 6 East 39th St., New York, for the Educational Department of the De Laval Separator Company.
These slides have been digitized and are available at https://www.flickr.com/search/?user_id=134017397%40N03&sort=date-taken-desc&text=altena&view_all=1