Justice Gray in United States v. Wong Kim Ark, 169 U. S. 649, 654:

"In this, as in other respects, it must be interpreted in the light of the common law, the principles and history of which were familiarly known to the framers of the Constitution. Minor v. Happersett, 21 Wall. 162; Ex parte Wilson, 114 U. S. 417, 422; Boyd v. United States, 116 U. S. 616, 624, 625; Smith v. Alabama, 124 U. S. 465. The language of the Constitution, as has been well said, could not be understood without reference to the common law. 1 Kent, Com., 336; Bradley, J., in Moore v. United States, 91 U. S. 270, 274."

In the argument on the demurrer counsel for plaintiff endeavored to show that Congress had expressly imposed the common law on all this territory prior to its formation into States. See also the opinion of the Supreme Court of Kansas in Clark v. Allaman, 71 Kansas, 206. But when the States of Kansas and Colorado were admitted into the Union they were admitted with the full powers of local sovereignty which belonged to other States, Pollard v. Hagan, supra; Shively v. Bowlby, supra; Hardin v. Shedd, 190 U. S. 508, 519; and Colorado by its legislation has recognized the right of appropriating the flowing waters to the purposes of irrigation. Now the question arises between two States, one recognizing generally the common law rule of riparian rights and the other prescribing the doctrine of the public ownership of flowing water. Neither State can legislate for or impose its own policy upon the other. A stream flows through the two and a controversy is presented as to the flow of that stream. It does not follow, however, that because Congress cannot determine the rule which shall control between the two States or because neither State can enforce its own policy upon the other, that the controversy ceases to be one of a justiciable nature, or that there is no power which can take cognizance of the controversy and determine the relative rights of the two States. Indeed, the disagreement, coupled with its effect upon a stream passing through the two States, makes a matter for investigation and

determination by this court. It has been said that there is no common law of the United States as distinguished from the common law of the several States. This contention was made in Western Union Telegraph Company v. Call Publishing Company, 181 U. S. 92, in which it was asserted that, as Congress having sole jurisdiction over interstate commerce had prescribed no rates for interstate telegraph communications, there was no limit on the power of a telegraph company in respect thereto. After referring to the general contention, we said (pp. 101, 102):

"Properly understood, no exceptions can be taken to declarations of this kind. There is no body of Federal common law separate and distinct from the common law existing in the several States in the sense that there is a body of statute law enacted by Congress separate and distinct from the body of statute law enacted by the several States. But it is an entirely different thing to hold that there is no common law in force generally throughout the United States, and that the countless multitude of interstate commercial transactions are subject to no rules and burdened by no restrictions other than those expressed in the statutes of Congress. Can it

be that the great multitude of interstate commercial transactions are freed from the burdens created by the common law as so defined, and are subject to no rule except that to be found in the statutes of Congress? We are clearly of opinion that this cannot be so, and that the principles of the common law are operative upon all interstate commercial transactions except so far as they are modified by Congressional enactment."

What is the common law? Kent says (vol. 1, p. 471): "The common law includes those principles, usages and rules of action applicable to the government and security of persons and property, which do not rest for their authority upon any express and positive declaration of the will of the legislature."

As it does not rest on any statute or other written declaration of the sovereign, there must, as to each principle thereof, be a first statement. Those statements are found in the deci

sions of courts, and the first statement presents the principle as certainly as the last. Multiplication of declarations merely adds certainty. For after all, the common law is but the accumulated expressions of the various judicial tribunals in their efforts to ascertain what is right and just between individuals in respect to private disputes. As Congress cannot make compacts between the States, as it cannot, in respect to certain matters, by legislation compel their separate action, disputes between them must be settled either by force or else by appeal to tribunals empowered to determine the right and wrong thereof. Force under our system of Government is eliminated. The clear language of the Constitution vests in this court the power to settle those disputes. We have exercised that power in a variety of instances, determining in the several instances the justice of the dispute. Nor is our jurisdiction ousted, even if, because Kansas and Colorado are States sovereign and independent in local matters, the relations between them depend in any respect upon principles of international law. International law is no alien in this tribunal. In The Paquete Habana, 175 U. S. 677, 700, Mr. Justice Gray declared:

"International law is part of our law, and must be ascertained and administered by the courts of justice of appropriate jurisdiction, as often as questions of right depending upon it are duly presented for their determination."

And in delivering the opinion on the demurrer in this case Chief Justice Fuller said (185 U. S. 146):

"Sitting, as it were, as an international, as well as a domestic tribunal, we apply Federal law, state law, and international law, as the exigencies of the particular case may demand."

One cardinal rule, underlying all the relations of the States to each other, is that of equality of right. Each State stands on the same level with all the rest. It can impose its own legislation on no one of the others, and is bound to yield its own views to none. Yet, whenever, as in the case of Missouri v. Illinois, 180 U. S. 208, the action of one State reaches through the agency of natural laws into the territory of another State, VOL. CCVI-7

the question of the extent and the limitations of the rights of the two States becomes a matter of justiciable dispute between them, and this court is called upon to settle that dispute in such a way as will recognize the equal rights of both and at the same time establish justice between them. In other words, through these successive disputes and decisions this court is practically building up what may not improperly be called interstate common law. This very case presents a significant illustration. Before either Kansas or Colorado was settled the Arkansas River was a stream running through the territory which now composes these two States. Arid lands abound in Colorado. Reclamation is possible only by the application of water, and the extreme contention of Colorado is that it has a right to appropriate all the waters of this stream for the purposes of irrigating its soil and making more valuable its own territory. But the appropriation of the entire flow of the river would naturally tend to make the lands along the stream in Kansas less arable. It would be taking from the adjacent territory that which had been the customary natural means of preserving its arable character. On the other hand, the possible contention of Kansas, that the flowing water in the Arkansas must, in accordance with the extreme doctrine of the common law of England, be left to flow as it was wont to flow, no portion of it being appropriated in Colorado for the purposes of irrigation, would have the effect to perpetuate a desert condition in portions of Colorado beyond the power of reclamation. Surely here is a dispute of a justiciable nature which must and ought to be tried and determined. If the two States were absolutely independent nations it would be settled by treaty or by force. Neither of these ways being practicable, it must be settled by decision of this court.

It will be perceived that Kansas asserts a pecuniary interest as the owner of certain tracts along the banks of the Arkansas and as the owner of the bed of the stream. We need not stop to consider what rights such private ownership of property might give.

In deciding this case on demurrer we said (185 U. S. 142), referring to the opinion in Missouri v. Illinois:

"As will be perceived, the court there ruled that the mere fact that a State had no pecuniary interest in the controversy, would not defeat the original jurisdiction of this court, which might be invoked by the State as parens patria, trustee, guardian or representative of all or a considerable portion of its citizens; and that the threatened pollution of the waters of a river flowing between States, under the authority of one of them, thereby putting the health and comfort of the citizens of the other in jeopardy, presented a cause of action justiciable under the Constitution.

"In the case before us, the State of Kansas files her bill as representing and on behalf of her citizens, as well as in vindication of her alleged rights as an individual owner, and seeks relief in respect of being deprived of the waters of the river accustomed to flow through and across the State, and the consequent destruction of the property of herself and of her citizens and injury to their health and comfort. The action complained of is state action and not the action of state officers in abuse or excess of their powers."

It is the State of Kansas which invokes the action of this court, charging that through the action of Colorado a large portion of its territory is threatened with disaster. In this respect it is in no manner evading the provisions of the Eleventh Amendment to the Federal Constitution. It is not acting directly and solely for the benefit of any individual citizen to protect his riparian rights. Beyond its property rights it has an interest as a State in this large tract of land bordering on the Arkansas River. Its prosperity affects the general welfare of the State. The controversy rises, therefore, above a mere question of local private right and involves a matter of state interest, and must be considered from that standpoint. Georgia v. Tennessee Copper Co., decided this day, post, p. 230.

This changes in some respect the scope of our inquiry. It is not limited to the simple matter of whether any portion of the