“the Northern Securities Company, the Great Northern Railway Company, the Northern Pacific Railway Company, and others, appellants, v. the United States, respondent : railway "mergers" operating a substantial division of territory the result of an irresistible trend or tendency in railway development : their inevitability as disclosed in the history of railway combination and amalgamation throughout the world : their consonance with public policy : their economic validity : constitutional considerations : argument amicus curiae”