Very closely related to the authority of the States to legislate with reference to commercial matters of a local character, is the power of the States, in the exercise of their police powers to enact and enforce measures which incidentally, but often substantially, affect interstate commerce.

The distinction that is drawn between these police powers of the States, and their authority to enforce local commercial regulations is that, in the absence of countervailing federal legislation, the latter are valid even though conceded to bear directly upon interstate or foreign commerce, whereas the police regulations are only valid bearing upon it is so remote that it cannot be termed in any just sense an interference. Within the second class of cases - those of what may be termed concurrent jurisdiction - are embraced laws for the regulation of pilots (Cooley v. Philadelphia Port Wardens, 12 How. 299; 13 L. ed. 996; Pacific -Mail SS. Co. v. Joliffe, 2 Wall. 450; 17 L. ed. 805; Ex parte McNiel, 13 Wall. 236; 20 L. ed. 624: Wilson v. McNamee, 102 U. S. 572; 26 L. ed. 234) ; quarantine and inspection laws and the policing of harbors (Gibbons v. Ogden, 9 Wheat, 1; 6 L. ed. 23; New York v. Miln, 11 Pet. 102; 9 L. ed 648; Turner v. Maryland, 107 U. S. 38; 2 Sup. Ct. Rep. 44; 27 L. ed. .370; Morgan's L. & T. R. & SS. Co. v. Louisiana Board of Health, 118 U. S. 455; 6 Sup. Ct. Rep. 1114; 30 L. ed. 237) ; the improvement of navigable channels (Mobile Co. v. Kimball, 102 U. S. 691; 26 L. ed. 236; Escanaba & L. M. Transp. Co. v. Chicago, 107 U. S. 678; 2 Sup. Ct. Hep. 185; 27 L. ed. 442; Huse v. Glover, 119 U. S. 543; 7 Sup. Ct. Rep. 313; 30 L. ed. 487) ; the regulation of wharves, piers and docks, (Cannon v. New Orleans, 20 Wall. 577: 22 L. ed. 417; Keokuk N. L. Packet Co. v. Keokuk. 95 U. S. 80, 24 L. ed. 377; Northwestern U. Packet Co. v. St. Louis, 100 U. S. 423; 25 L. cd. 688; Cincinnati. P. B. S. & P. Packet Co. v. Catlettsburg, 105 U. S. i 26 L. ed. 1 : Parkersburg & O. R. Transp. Co. v. Parkersburg, 107 U. S. 691 : 2 Sup. Ct. Rep. 732; 27 L. ed. 584; Ouachita & M. R. Packet Co. v. Aiken, 121 U. S. 444: 7 Sup. Ct. Rep. 907; 30 L. ed. 976) ; the construction of dams and bridges across navigable waters of a State (Wilson v. Black Bird Creek Marsh Co., 2 Pet. 245; 7 L. ed. 412; Cardwell v. American River Bridge Co.. 113 U. S. 205; 5 Sup. Ct. Rep. 423; 28 L. ed. 959; pound v.. Truck, 95 V. S. 459; 24 L. ed. 525), and the establishment of ferries (Con-May v. Taylor, 1 Black, 603). But wherever such laws, instead of being of a local nature and not affecting interstate commerce but incidentally, are national in their character, the non-action of Congress indicates its will that such commerce shall be free and untrammeled, and the case falls within the third class - of those laws wherein the jurisdiction of Congress is exclusive (Brown v. Houston, 114 U. S. 622; 5 Sup. Ct Rep. 1091; 29 L ed. 257: Bowman v. Chicago & N. W. R. Co., 125 U. S. 465; 8 Sup. Ct. Rep. 689; 31 L. ed. 700.)" when their influence upon interstate or foreign commerce is an incidental, indirect one. In other words, as to matters of local concern, the States are recognized to have a concurrent legislative power in the fields of interstate and foreign commerce; while as to police measures (and the same is true as to tax laws or other state laws for the regulation of domestic commerce) the States have an authority which is not concurrent with that of the United States, but which is, when kept within its proper sphere, exclusive of federal control. Thus, local regulations even though they operate directly upon interstate and foreign commerce are valid unless and until there is federal legislation concerning the same subject. Tax laws, laws for the regulation of domestic commerce and police regulations, upon the other hand, have no constitutional validity whatever if they operate directly and primarily as a restraint upon interstate or foreign commerce as such.

To the writer it would seem that the foregoing distinction between the concurrent local legislative powers and the police powers of the States with reference to interstate and foreign commerce is an unnecessary and confusing one, for the fact is to be noted that all of the local regulations which have been referred to in the preceding section may properly be described as police regulations and justified as such. If, and when, so justified, it will be possible for the courts, without changing substantially the effect of its holdings, to accept finally and completely the doctrine of the exclusiveness of the federal authority over interstate and foreign commerce, and base the validity of local state commercial regulations not upon a state concurrent legislative power as to local matters, but upon the States' police or other reserved powers.56a However, the courts still recognize the distinction between the two sources of state power to affect interstate commerce by their legislation, and this practice is, therefore, here followed.

That a state law which, in its essential nature, is a legitimate exercise of the police power is not rendered invalid by reason of the fact that interstate commerce is thereby incidentally affected is well established.

56a See Cooke, Commerce Clause, § 55.

In Hennington v. Georgia,57 in which case was upheld the validity of a state statute prohibiting the running of freight trains on Sundays, the court, after a review of adjudged cases, say: "These authorities make it clear that the legislative enactments of the States, passed under their admitted police powers, and having a real relation to the domestic peace, order, health, and safety of their people, but which, by their necessary operation, affect to some extent or for a limited time the conduct of commerce among the States, are yet not invalid by force alone of the grant of power to Congress to regulate such commerce, and, if not obnoxious to some other constitutional provision or destructive of some right secured by the fundamental law, are to be respected in the courts of the Union until they are superseded and displaced by some act of Congress passed in execution of the power granted to it by the Constitution. Local laws of the character mentioned have their source in the powers which the States reserved, and never surrendered to Congress, of providing for the public health, the public morals, and the public safety, and are not, within the meaning of the Constitution, and considered in their own nature, regulations of interstate commerce simply because, for a limited time or to a limited extent, they cover the field occupied by those engaged in such commerce. The statute of Georgia is not directed against interstate commerce. It establishes a rule of civil conduct applicable alike to all freight trains, domestic as well as interstate. It applies to the transportation of interstate freight the same rule precisely that it applies to the transportation of domestic freight."56

57 163 U. S. 299; 16 Sup. Ct. Rep. 1086; 41 L. ed. 166.

58 This equality of treatment of interstate and domestic commerce is not, it is to be observed, an infallible test as to the validity of state law affecting interstate commerce. Thus in Robbins v. Taxing District of Shelby Co. (120 U. S. 489; 7 Sup. Ct. Rep. 592; 30 L. ed. 694) the court were obliged to abandon this rule. The court there say: "It is strongly urged, as if it were a material point in the case, that no discrimination is made between domestic and foreign drummers - those of Tennessee and those of other States - that all are taxed alike. But that does not meet the difficulty. Interstate commerce cannot be taxed at all, even though the same amount of tax should be laid on domestic commerce, or that which is carried on solely within the State. This was decided in the case of The State Freight Tax Cases (15 Wall. 232; 21 L. ed. 146)."

This interference with interstate and foreign commerce, it is to be emphasized, is permitted only when the necessities and the convenience of the public seem to demand it and when the regulation provided for is a reasonable and just one. In other words, the States may not, under the guise of an exercise of their police powers, attempt what in effect amounts to a direct regulation of interstate and foreign commerce, or impose an unnnecessary or arbitrary burden upon interstate carriers. As will later appear the same principle applies to the exercise of the other powers of the States, as for example, the power to tax, or to regulate domestic commerce. In the exercise of these powers it is often the case that interstate and foreign commerce are indirectly and even substantially affected. But in no case can regulation of interstate and foreign commerce be the direct or primary aim of the State's action. If this is the aim or effect, no support for the validity of the law may be obtained by calling the law a police regulation. "The substantial question in any given case is," say the court in Henderson v. Mayor,59 " whether or not there is a valid exercise of a power reserved to the States, whether or not within the scope of the 'police power.' It has been well said as to the police power, that' no definition of it and no urgency for its use can authorize a State to exercise it in regard to a subject-matter which has been confided exclusively to the discretion of Congress by the Constitution. Nothing is gained in the argument by calling it the police power.' " 60

An interesting and recent case in which it is shown that the court will not permit interstate carriers to be subjected to unnecessary or unreasonable police regulations is Houston, etc., R. R. Co. v. Mayes.61 In this case it was held that a state law which penalized the failure of a railway company to furnish shippers with cars within a certain number of days after notice, and permitted no excuse except inability arising from strikes or other public calamity, was unconstitutional in so far as it applied to interstate carriers. The court say: "Although it may be admitted that the statute is not far from the line of proper police regulation, we think that sufficient allowance is not made for the practical difficulties in the administration of the law, and that, as applied to interstate commerce, it transcends the legitimate powers of the legislature."

59 92 U. S. 259; 23 L. ed. 543.

60 Cf. L. S. & M. S. Ry. Co. v. Ohio, 173 U. S. 285; 19 Sup. Ct. Rep. 465; 43 L. ed. 702.

61 201 U. S. 321; 26 Sup. Ct. Rep. 491; 50 L. ed. 772.

It is thus evident that the federal court will examine a state police regulation not only with reference to the fact whether or not it amounts to a direct regulation of interstate commerce, but whether its provisions are in themselves sufficiently reasonable, practicable, and just, as to furnish an excuse and justitication for the incidental interference with interstate commerce which their enforcement will necessitate.

Finally, with reference to the police powers of the States and interstate commerce, it is to be observed that however incidental their direct upon such commerce they have, of course, no validity in so far as they conflict with existing federal statutes. In Houston v. Mayes62 the court say: "Of course such [police] rules are inoperative if conflicting with regulations upon the same subject enacted by Congress."