PREFACE. While this is a second edition of a book published in 1888, it is to a great extent a new book. The text has been not only revised, but largely rewritten. The text is exclusively my work, but the references in the notes to the later cases are entirely the work of Mr. Reeder, who has prepared the table of cases and the index, and who has kindly read all the proofs. My hearty acknowledgments are due to Mr. Reeder for the valuable assistance which he has rendered to me, and also for very many pertinent suggestions which I have adopted, and which have given to the text much of any value it may have. C. S. P. Philadelphia, 1st Oct., 1904. CONTENTS. 9. The necessity of their existence. 10. Their constitutional recognition. 11. The test of the relation of the means to the end. 24. Expressed restraints upon state taxation. 25. Implied restraint upon state taxation resulting from the federal 27. State taxation as affected by the prohibition of the impairment of 28. State taxation as affected by the grant to Congress of the power of |