In Southworth v. United States, the Supreme Court dealt with a case involving the interpretation of tariff laws. The plaintiff, Southworth, imported iron from Sweden and was charged an import duty based on its weight. However, he argued that according to the Tariff Act of 1890 (also known as McKinley Tariff), he should have been charged only for the actual iron content excluding any foreign substances mixed in it during transportation or storage. The court ruled against him stating that Congress intended to levy duties on gross weight rather than net weight since it was impractical to determine exact iron content due to varying impurities present in different shipments. Thus, they upheld customs officials' right to charge tariffs based on total shipment weight including any non-metallic elements such as moisture or rust.

The dissenting opinion in the Southworth v. United States case argued that the government did not have sufficient evidence to prove that Southworth was guilty of conspiracy to defraud the United States. The dissenting justices believed that while there may have been suspicious circumstances surrounding his actions, these alone were not enough to establish guilt beyond a reasonable doubt. They contended that mere association with known criminals or presence at the scene of a crime does not necessarily make one complicit in it. Furthermore, they pointed out inconsistencies and contradictions within testimonies used against Southworth which further cast doubts on his conviction. Therefore, they concluded that he should be acquitted due to lack of substantial proof.