Me. Justice Field
delivered the opinion of the court.
. The several positions.taken by the appellant for the reversal" of the decree of the Circuit Court may be resolved .into these four: 1st, That.the- act of the legislature of Alabama of Feb. 1.6, 1867, "to provide for the improvement of the" river, bay, and harbor of Mobile," is invalid, in that it conflicts with the" •commercial power vested in Congress; 2d, that if the act be not, for this reason, invalid, the expenses for the work authorized by it could not, under the Constitution of the State then in force, be imposed upon the county of Mobile, the work being for" the benefit of the whole State-; 3d, that the right of the complainants to relief is barred .by a previous, adjudication in the courts of the State against their claim; and, 4th, that the case presented by the bill is not one for the cognizance of a - court of, equity. Eách of these .positions merits special, consideration. •
1. The act of Feb. 16, 1867, created a board of! commission^ ers for the improvement of the river, harbor, and bay of Mobile, and required the president of the commissioners of revenue of Mobile County to issue bonds to the amount of $1,600,00.0, and deliver them, when, called for, to the- board, tomeet the expenses of the work directed. The board was authorized to apply the bonds, or their proceeds, to the cleaning; out, deepening, and widening of the river, harbor, and bay of Mobile, or any part thereof, or to the construction of an artificial harbor in addition to such improvement. '
In' June, 1872, the board of commissioners entered into a contract with the complainants, Kimball and Slaughter, to dredge and cut a channel through a designated bar ;in the bay,' of specified width, depth, and distance, at a named price- per cubic yarcl of material excavated and removed, and to receive in payment the bonds of the county, issued under the act mentioned, atthg rate of 82|- cents on the dollar. In pursuance of this contract, the'work agreed'upon.was at. once undertaken by the complainants, and was completed by them in .March, 1873, and accepted by the board through' its authorized engineer. The amount due to them was paid, with the exception of seventeen bonds. The'board gave them a certificate that they were entitled to that number of bonds, and, after some delay, delivered eleven to them. It is to obtain a delivery of the. remaining six, or payment of their valué, that the present suit is brought.
The objection that the law of the State, in authorizing the improvement of the harbor of Mobile, trenches upon the commercial power of Congress, assumes an exclusion of State authority from all subjects in 'relation to whioh that power maybe exercised, not warranted by the adjudications' of. this court, notwithstanding the strong expressions used by some" of its judges. That power is indeed without limitation. It authorizes Congress to prescribe 'the conditions upon which commerce in all its forms shall.be conducted between our-citizens and the. citizens or subjects of other countries, and between the citizens of the several States, and to adopt measures to promote its growth and insure its safety. Andas commerce embraces' navigation, the improvement- of harbors and bays along our coast, and.of navigable rivers within the States connecting with them-, falls .within the power. The subjects, indeed, upon which Congress can act under- this power are Of infinite variety, requiring for their successful management different plans or modes of treatment. . Some of them are, national in their char-acter,'and. .admit and require uniformity of regulation, affecting alike all the States; • others are local, or are mere aids to commerce, and can only be properly regulated by provisions adapted to their special circumstances and localities. Of the former class'-may be mentioned all that, portion of commerce with foreign countries or between the States which consists in the transportation,' purchase, sale, and' exchange of commodities. Here .there can of necessity be only one system or plan of regulations, and that Congress alone can-prescribe. Its non-action, .in such cases with respect to any particular commodity or mode of transportation, is a declaration of its purpose that the commerce' in that commodity or by that means of .transportation shall'be ¿'free: There would otherwise-bé no security against. conflicting regulations of different States, each discriminating in favor of its own products and citizens, and against the products and citizens of other States. . And it is a matter of public history that the object of -testing in Congress the power to regulate commerce-with foreign nations and among the States-was to insure uniformity of regulation against conflicting and discriminating State legislation.
Of the cjass of subjects local in their nature, or intended as m.ere aids to commerce, which are best provided for by special regulations, may be mentioned harbor pilotage, buoys, and beacons to guide mariners to tbe proper channel in which to direct their vessels.
The rules to govern harbor pilotage must depend in a great degree upon the peculiarities of the ports where they are to be enforced.. It has. been found by experience that skill and effi.ciency on the part of local pilots is best secured by leaving this subject principally to the control of the States. Their authority to act upon the matter and'regulate the whole sub .ject,. in the absence of legislation by Congress, has been recognized by this court in- repeated instances. In Cooley v. Board of Wardens of the Port of Philadelphia, the court refers to the act of Congress of 1789, declaring that pilots should continue to be regulated by such laws as the States might respectively thereafter enact for that purpose, and observes that " it manifests the understanding -of Congress, at the outset of the government, that the nature of-this subject is not such as to. require its exclusive legislation. The practice of the States and of the' national government has been in conformity with this declaration, from the. origin of the national government to. this time; and thé nature of the subject, when examined, is such as to leave no doubt ,of the superior fitness'and propriety, not to say the absolute necessity, of different systems of regulation, drawn from local knowledge and- experience and conformed to local wants.." 12 How. 299, 320.
Buoys and beacons are important aids, and sometimes are essential to the safe navigation of vessels, iñ indicating the channel to be followed at the entrance of-harbors and in rivers, and their establishment by Congress is undoubtedly within its commercial power. . But it would be extending -that power to the exclusion of State authority to an unreasonable degree to hold that whilst it remained unexercised upon this .subject, it> would be unlawful for the State- to provide the buoys and beacons required for the safe navigation of its harbors and riversj and in case of their .destruction by storms or otherwise it could not temporarily supply their places until Congress could act in the matter and provide for their Te-establishment. That power which every State possesses, sometimes termed its police power,' by which it legislates for the protection of the lives, health, and property of its people, would' justify measures of this kind."
The uniformity of commercial regulations, which the grant to Congress was designed to secure against conflicting State provisions, was necessarily intended only for cases where, such. uniformity is practicable. Where from the nature of the subject dr the sphere of its operation the case is local and limited, special 'regulations adapted to the immediate locality could only have been contemplated. State action upon such Subjects can constitute no interference with the commercial power of Congress, for when that acts the State authority is superseded. Inaction of Congress upon these subjects of a local nature or operation,' unlike its inaction upon matters affecting all the. States and requiring uniformity of regulation, is not to be taken as a declaration that nothing shall be done with respect to them, but is rather to be deeméd a declaration that for the tim.e being, and until it sees fit to act, they may be regulated by State authority.
The improvement of. harbors, bays,- and navigable rivers within the States falls within this last category of cases. The control of Congress over them is to insure freedom in their navigation, so far as that is essential'to the exercise-of its commercial power. Such freedom is not encroached upon by the removal of Obstructions to their navigability, or by other legitimate improvement. The States have as f-ull control over their purely internal commerce as' Congress has over commerce among the several States and with foreign nations; and to promote the growth of that internal commerce and insure its safety they have an undoubted right to remove obstructions from their harbors and rivers, deepen their channels, -and improve them generally, if they do not impair their free navigation as permitted under the laws of the United States, or defeat any system for- the improvement of -their navigation provided by the general government. Legislation of the States for the purposes and within the limits mentioned'do not infringe upon the commercial power, .of Congress ; and so we hold that the act of the State pf Alabama of Feb. 16, 1867, to provide for the "improvement of the river, bay, and harbor .of Mobile," is riot invalid.
There have been, it is true, expressions by individual judges of this court, going to the length that the' mere grant of the commercial power, anterior to any action of Congress under it, is exclusive of all State authority; but there haS been no. adjudication of the court to that effect. In the opinion of the court in Gibbons v. Ogden, the first, and leading case upon the construction of the commercial clause of the Constitution, and-which opinion is recognized as one" of the ablest of the great Chief Justice then presiding, there are several expressions which would indicate, and his general reasonirig' would tend to the same conclusion, that in his judgment the grant of the' commercial power was of itself sufficient to exclude all action of the States; and it is upon them that the. advocates of the exclusive theory chiefly rely;, and yet he takes care to observe ' that the question was not involved in the- decision required by that case. " In discussing the question whether this power is still in the States," he observes that, "in the case under consideration, we may dismiss from it the inquiry, whether it is surrendered by the mere grant to Congress, or is retained -until'Congress. shall exercise the power. We may dismiss that inquiry, because it has been exercised, and the regulations which Congress deemed it proper to make are now in full •operation. The sole question is, Can a State regulate commerce with foreign nations and among the several States while Congress is regulating it?" And the decision was necessarily restricted by the limitations of the question presented. . It determined that.the grant of power by the Constitution, accompanied by legislation, Under it, operated as an inhibition upon the States from interfering with the subject of, that legislation. The acts of New York giving to Livingston and Fulton an exclusive right to navigate all the waters within its jurisdiction, with' vessels propelled by steam, for a certain period, being in collision with the laws of Congress regulating the coasting trade, were, therefore, adjudged to be unconstitutional. This judgment was rendered in 1824. 9 Wheat. 1. Some years later (1829) the case of Willson v. Blackbird Creek Marsh Company came before the court. There a law of Delaware authorizing the. construction of a bridge over one of its small navigable streams, which obstructed the navigation of the stream, was held not to be repugnant to the commercial power of Congress. The court, Chief Justice Marshall delivering- its., opinion, placed its decision entirely upon the absence' of any congressional legislation on the subject. Its language was: " If ' Congress had parsed any act which bore upon the case ; any act in .execution, of the power to regulate commerce, the object of which was to control .State legislation' over those small jiavigable creeks into which the tide-flows, and which abound throughout the lower country of the Middle and Southern .States, — we should not feel much difficulty in saying that a State law coming in conflict with such act would be void. But, Congress has passed no such act. -The'repugnancy of theflaw of Delaware to the Constitution 'is placed entirely on its repugnancy to the power to regulate commerce with' foreign nations and among the several States,— a power which has not .been so exercised as to affect, the question." 2 Pet. 245, 252.
In the License Oases, which were before the court in 1847, there was great diversity of views in the opinions of the different judges upon the operation of the grant of the commercial power of Congress in' the' absence of congressional legislation. Extreme-doctrines upon both sides of the question were asserted by some of the judges, but the decision reached, so far as it can be viewed as determining any question of construction, was confirmatory of the doctrine that legislation df Congress is, essential to prohibit the action Of the States upon the subjects there considered.
But in 1851, in the'case of Cooley v. Board of Wardens of the Port of Philadelphia, to which we have- already referred, the attention of the court appears to have • been for- the first time drawn to the varying and different regulations required by the different subjects, upon which Congress may legislate under the commercial power; and from- this consideration the conclu-T sion was reached, that, as some of these subjects are national in their nature, admitting of one uniform plan' Or. system of regulation, whilst others, being local in their nature or oper— ation, ,can be best regulated by the States, the exclusiveness of the power in any case is to be determined more by the nature of the subject upon which it is to operate than by the terms of the grant, which, though general, are not accompanied by any express prohibition to the exercise of the power by the States. The decision was confined to the validity of regulations by the States of harbor pilotage; but the reasoning of the court suggested as satisfactory a solution as perhaps could be obtained of the question which had so long divided the judges. The views expressed in the opinion delivered are follpwed in Gilman v. Philadelphia (3 Wall. 713), and are mentioned with approval in Crandall v. State of Nevada, 6 id. 35. In the first of these cases, the court, after stating that some subjects of commerce call for uniform rules and' national legislation,- and that others can "be best regulated by rules and provisions suggested by the varying circumstances of different localities, and limited in their operation to such localities respectively," says, " whether the power in any given case js vested exclusively in. the general government- depends upon the nature of ,the subject to be regulated." This doctrine was ' subsequently recognized in the case of- Welton v. State of Missouri (91 U. S. 275), in Henderson v. Mayor of New York (92 id. 259), and in numerous other cases; and it may be considered as expressing the final judgment of the court.
Perhaps some of the divergence of views upon this question among former judges may have arisen from not always bearing' in mind the distinction between commerce as strictly defined, and its local aids or- instruments, or measures taken for its improvement. Commerce with foreign countries and among the States, strictly considered, consists in intercourse and traffic, including in these terms navigation and the transportation and transit of persons and property, as well as the purchase, sale, and exchange of commodities. For the regulation of commerce' •as thus defined there can.be only one system of rules applicable alike to the whole country; and the authority which can act for the whole country can alone adopt such a system; Action upon it by sepárate States is not, therefore, permissible. Language affirming the exclusiveness of the grant of power over commerce as thus defined may not be inaccurate, when it.would be so if applied to legislation upon subjects which are merely auxiliary to commerce,
2. The second objection of the appellant to the decree of the Circuit Court is equally as untenable as the first. The question of the validity' of the act of Feb. 16, 1867, under the Constitution of Alabama at the time in force, was before the Supreme Court of the State in 1871. It was contended that the act contravened the article which forbade' the taking of private, property for public use without just- compensation, or for private use, or the use of corporations other than municipal,, without the"consent of the.,owner, and the article- which restrained the legislature .from delegating power to levy taxes to individuals or private corporations. The court held that.the act was not open to objection on either of these grounds, except perhaps in the clanse which authorized the board of commissioners to assess dues or tolls to be collected on vessels or water-craft; and if that clause could be deemed a delegation of the taxing power under the article mentionéd, that portion only of the act was invalid. The issue by the president and commissioners of revenue of Mobile County of bonds for the - improvement of the river, bay, and harbor of Mobile was.not a talcing of private property for public use, within the meaning of . the constitutional, clause. It was a loan of the. credit of the county for a work public in its character,' designed to'be of' general benefit to the State, but more especially and immediately to the county. The expenses of the work were of course to be 'ultimately defrayed by taxation upon the property and people of the county. But neither is taxation for a public purpose', however great, the taking of private property for public use, in the sense of the Constitution. Taxation only exacts a contribution from individuals of the State or of a particular district, for the'support of the government,'.or. to meet some public expenditure authorized by it, for which they receive' compensation in the protection which government affords, or in the benefits of the special expenditure. But when private property is taken for public use, the owner receives full compensation. The taking differs from a sale by him only in that the transfer'of title may be compelled, and the amount of compensation be determined by a jury or officers of the government - appointed for that purpose. In the one case, the party bears'' only a.'share of the public burdens; in the other, he exchanges his property for its equivalent in money. The two things are essentially different.'.
The objection to tbe act here raised is different from that taken in the State court. Here the objection urged is that 'it fastens upon one county the expense of. an improvement for the benefit of the whole State. Assuming this to beso, it is not an objection which destroys its validity. When any public work is authorized, it rests with the legislature, unless restrained by constitutional provisions, to determine in' what manner the means to defray its cost shall be raised. It may apportion the burden ratably among all the counties, or other particular 'subdivisions of the State, or lay the greater share or the whole upon that county or portion of the State specially and immediately benefited by the expenditure.
' It may be that the act in imposing upon the county of Mobile the entire burden of improving the river, bay, and harbor of Mobile is harsh and oppressive, and that it would have been more just to the people of the county if the legislature had apportioned-the expenses of the improvement, which was to benefit the whole State, ainong all it's counties. But this court is not the harbor, in which the people of a city or' county can find a refuge from ill-advised, unequal, and oppressive State legislation. The judicial power of the Federal government can only be invoked when some right under the Constitution, laws, or treaties of the United States is invaded. In all other cases, the only remedy for the evils complained of rests with the people, and must be obtained through a change of their representatives.- They must select agents who will correct the injurious-legislation, so far as that is practicable, and be more mindful than their predecessors of the public interests.
3. The objection that the right of the complainants to relief is barred by a previous adjudication in the courts of the State against their claim arises in this wise: After the complainants had performed their work on the harbor of Mobile under the contract with the harbor commissioners, of June, 1872, and the work had been approved and accepted, the legislature passed the act of April 19, 1873-, to regulate the further proceedings of the board* restricting the issue of bonds to the amount, including those already issued, of $200,000, and declaring that the harbor board should not, under any pretence whatever, be entitled to receive bonds to any greater amount. Bonds to that amount had already been delivered to the board, and for -six of them, the number to which they were entitled, the complainants applied. The delivery of the bonds béing refused, they, brought suit against the county of Mobile to obtain them or their value.
/ Two grounds were alleged on which the responsibility of the' county was asserted : one, that the harbor board had ceased to have anything to do with the improvement of the river, bay, and harbor of Mobile, and had turned over all the money and bonds left in''its possession to the officials of the county; the other, that the county through-its officials had bought from the harbor ' board, thirty-one of the two hundred bonds issued, at a priee. less than their market value,, and had refhsed to deliver to the: complainants the six due to them which they had demanded.
The District Court gave a decree for the complainants, but the Supreme Court reversed it, holding that upon the first ground the complainants were mistaken as to the situation' of the harbor board, and that it continued to. exist for the purpose of winding up and Settling its business; arid upon the second ground, that although thirty-one of the bohds had been purchased as stated, they had been cancelled before the complainants made the demand'for six of them; and it was shown by the county that there- still remained with the harbor board unaccounted for twenty-three of the two hundred bonds,, which were more than sufficient to pay the complainants and other debts which the board owed. The court therefore decided that the delinquency complained' of was that of the harbor board and not of the county; 'that the only obligations imposed upon the county were that it should issue its bonds upon' the demand of the harbor board, and pay them according to their stipulations; and as it appeared that the county officials had delivered to the board.the whole amount-of the bonds demanded, and that this amount was ample for the fulfilment of the obligations contracted for, the' suit, could not be maintained. The decree was, therefore, reversed and the bill dismissed, but .without prejudice, — a condition which prevented the adjudication from operating as a bar to the same claim,' if the complainants could in another suit obviate the defects of thé existing bill. In the present suit they have obviated these defects. They allege and prove that the harbor board had disposed of all the bonds it had received before the passage of the act of April 19, 1873, restricting the number to be issued, and that it had turned over to the officials of the county neither bonds nor proceeds to meet the demand of the complainants. The two suits, though seeking the same relief, test upon a different state of facts, and. the adjudication in the one constitutes, therefore, no bar to a recovery in the other.
4, But it is finally objected that the case presented by the bill is not .one for the cognizance of a court'of equity. This objec tion is important, only from the siippos.ed effect of the decision of the Supreme Court of the State in the first suit against the county brought, by the complainants. It appears to have been taken for granted by counsel, and also by the court below, that the Supreme Court of the State had decided that the harbor board was not the-agent of the county in making the contract with the complainants. We do hot so read its opinion. It only says that the board was created by the General Assembly of the State, and was nót an agent appointed by the county of Mobile. ' It does not state that the board was not an agent of the county, but only. that, its appointment was not from the county, and that it drew its existence and authority from the statute of the State.' It is not necessary to constitute an agency of á political subdivision of a State that its officials should be elected by its people or be appointed with their assent. It is enough to give them that character that, however appointed, they are authorized by law to act for the county,. district, or other political subdivision. Hqre, the harbor board, created by a law of the State, was authorized to' make contracts for a public work in which the county was specially interested, and by which it would be immediately'and directly benefited, and.to require obligations of the county to meet the expenses incurred.'' It is'a* mere báttle of words to contend that it was; or was not* an agent of. the county because its members were appointed by some exterior authority. It is enough' in 'this case that by force'of-the law of its creation it could bind the -county *f or work for which it contracted. Having thus bound the. county, the contractors are entitled 'to the .bonds stipulated,. or their equivalent in money. . If for any cause, the repeal- of the law creating'the harbor board, or the refusal of its members or other officials to act, the contract cannot be specifically enforced, a court of equity will order compensation in damages from the party ultimately liable. That court will free the case from all technical embarrassments, to the end that justice may be done to those who have trusted to the law, and the responsibility of parties. receiving', benefits, under it. The case here is not different in principle from the ordinary case of a"party being unable to comply with his contract when specific performance is demanded. If, for example, there be. a contract for: the pur chase-of land with which the purchaser has complied, but in which the vendor has failed, a court of equity will take jurisdiction ; and if it be seen that the vendor, from subsequent sales or otherwise, cannot comply with a-decree for a-specific performance, the court will adjudge compensation in damages. So, here, the court will grant the relief which, the complainants, under their contract, are entitled to have, if such relief can be obtained-from the county; but if "by reason of intervening obstacles- since the contract was made whether arising from laches or default of its officials or repealing legislation, this cannot be secured, an alternative and compensatory decree, that is, one for a monéy equivalent in the form of damages, will be directed. And as this has been done in the present, case, the decree is
Affirmed.