The Eddy was a Supreme Court case from 1866 that dealt with the issue of whether a state court could issue a writ of habeas corpus to a federal court. The case arose when a man named William Eddy was arrested in California for violating a federal law. Eddy sought a writ of habeas corpus from the California Supreme Court, which was denied. Eddy then appealed to the U.S. Supreme Court. The Supreme Court held that the California Supreme Court did not have the authority to issue a writ of habeas corpus to a federal court. The Court reasoned that the writ of habeas corpus was a federal prerogative and that the state court did not have the power to interfere with the federal court's jurisdiction. The Court also held that the writ of habeas corpus was a fundamental right that could not be denied by a state court. The Eddy case established the principle that state courts do not have the authority to issue writs of habeas corpus to federal courts. This decision has been cited in numerous subsequent cases and is still an important part of the law today.

In the case of The Eddy, the Supreme Court was asked to decide whether a state court had jurisdiction over a dispute involving two vessels that were registered in different states. Justice Field delivered the dissenting opinion, arguing that while it is true that each state has exclusive authority over its own vessels and their owners, this does not mean they have absolute power to determine all matters relating to them. He argued further that when disputes arise between vessels from different states, there must be some form of federal regulation or oversight in order for justice to be served fairly and equitably. In his view, Congress should provide such regulations so as to ensure uniformity among all states with regard to maritime law. Ultimately he concluded by stating that if no such federal laws exist then any decision made by one state's courts would only apply within its borders and could not bind another state's citizens or ships outside of those boundaries.