Undated, ca. 1926-1930 based on contemporary ads and mention of the "Sesquicentennial Grand Prize." Printed letter, business reply card, and illustrated broadsheet in original mailing envelope. Original creasing, light soil to mailing envelope, Very Good. Direct mail advertising for The Book of Knowledge, a children's encyclopedia mailed directly to the home, available in six languages: English, French, Italian, Spanish, Portuguese and Chinese. The letter includes a promising list of curious questions in the left column (Why is the sea never still? Why are tears salt? Is a stone alive?) and promises parents that their children "will devour it from cover to cover."