United States. Department of the Treasury. "Duties of Articles sent hither in Mail Bags, Including Books," in United States. Department of the Treasury. "Annual Report of the Secretary of the Treasury on the State of the Finances for the Year 1886, Volume II: Collection of Duties," Annual Report of the Secretary of the Treasury on the State of the Finances (1886) : 42-44. https://fraser.stlouisfed.org/title/194/item/5531/toc/38760 , accessed on March 28, 2024.