Powers v. Comly was a United States Supreme Court case that addressed the issue of whether a state court had the authority to issue a writ of habeas corpus to a prisoner held in a federal prison. The case arose when the petitioner, Powers, was convicted of a crime in the state of Pennsylvania and sentenced to a term of imprisonment in a federal prison. Powers then filed a petition for a writ of habeas corpus in the state court, seeking to be released from the federal prison. The state court granted the writ, and the federal government appealed the decision to the Supreme Court. The Supreme Court held that the state court did not have the authority to issue a writ of habeas corpus to a prisoner held in a federal prison. 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 government's authority to imprison individuals. The Court also noted that the writ of habeas corpus was a remedy for individuals who were unlawfully detained, and that the state court had no authority to determine whether the petitioner was being held lawfully or not. The Supreme Court's decision in Powers v. Comly established that state courts do not have the authority to issue writs of habeas corpus to prisoners held in federal prisons. The decision also clarified the scope of the writ of habeas corpus and the limits of state court authority in this area.

In the case of Powers v. Comly, the Supreme Court was tasked with determining whether a state court had jurisdiction to hear an appeal from a decision made by a federal district court in Pennsylvania. The majority opinion found that it did not have such authority and dismissed the appeal. However, Justice Field dissented from this ruling on two grounds: first, he argued that Congress had given state courts concurrent jurisdiction over appeals arising out of decisions made by federal district courts; second, he contended that even if Congress had not done so explicitly, they should be assumed to have intended for states to possess such power due to their inherent sovereignty as part of our nation's dual-sovereignty system. In conclusion, Justice Field maintained his belief that state courts were entitled to exercise appellate jurisdiction over cases originating in federal district courts and thus disagreed with the majority opinion which held otherwise.