In Mosher v. St. Louis, Iron Mountain and Southern Railway Company, the Supreme Court of the United States was asked to decide whether a railroad company was liable for damages caused by a train accident. The plaintiff, Mosher, was a passenger on the train when it collided with another train, resulting in serious injuries to Mosher. Mosher sued the railroad company, claiming that the company was negligent in its operation of the train. The Supreme Court held that the railroad company was liable for the damages caused by the accident. The Court found that the railroad company had a duty to exercise reasonable care in the operation of its trains, and that it had breached this duty by failing to take proper precautions to prevent the accident. The Court also held that the railroad company was liable for the damages caused by the accident, even though the accident was caused by the negligence of another train's engineer. The Court's decision in this case established that railroad companies have a duty to exercise reasonable care in the operation of their trains, and that they can be held liable for damages caused by their negligence. This decision has been cited in numerous subsequent cases involving railroad accidents.

In Mosher v. St. Louis, Iron Mountain and Southern Railway Company, the Supreme Court was tasked with determining whether a railroad company could be held liable for damages caused by its negligence in failing to provide adequate safety measures on its premises. Justice Field delivered the dissenting opinion of the court, arguing that while it is true that railroads have an obligation to use reasonable care in protecting their passengers from harm, they are not required to take extraordinary precautions beyond what is necessary for ordinary safety purposes. He argued that if such a requirement were imposed upon them then it would place an undue burden on them and would lead to increased costs which may ultimately be passed onto consumers through higher fares or freight rates. Furthermore, he noted that there had been no evidence presented at trial as to how much additional cost would have been incurred by implementing further safety measures than those already present at the time of this incident; thus making it impossible for him or any other justice on the court to determine whether such extra precautionary steps should have been taken or not.