Opinion of the Court. New Jersey v. Yard, 95 U. S. 104; Asylum v. New Orleans, 105 U. S. 362. If, however, the charter contain a reservation of an unlimited power to alter, amend or repeal, the legislature may take away an immunity from taxation. Tomlinson v. Jessup, 15 Wall. 454. Within the same principle are grants of an exclusive right to supply gas or water to a municipality, or to occupy its streets for railway purposes. New Orleans Gas Co. v. Louisi ana Light Co., 115 U. S. 650; New Orleans Water Works v. Rivers, 115 U. S. 674; Louisville Gas Co. v. Citizens' Gas Co., 115 U. S. 683; St. Tammany Water Works v. New Orleans Water Works, 120 U. S. 64; Boston & Lowell Railroad v. Salem & Lowell Railroad, 2 Gray, 1. So, if a company be chartered with power to construct and maintain a turnpike, erect toll-gates and collect tolls, such franchise is protected by the Constitution. Turnpike Co. v. Illinois, 96 U. S. 63; Monongahela Navigation Co. v. United States, 148 U. S. 312. If it be provided in the charter of a bank that the bills and notes of the institution shall be received in payment of taxes or of debts due to the State, such undertaking on the part of the State constitutes a contract between the State and holders of the notes, which the State is not at liberty to break, although notes issued after the repeal of the act are not within the contract, and may be refused. Woodruff v. Trapnall, 10 How. 190; Paup v. Drew, 10 How. 218; Furman v. Nichol, 8 Wall. 44; Keith v. Clark, 97 U. S. 454; Antoni v. Greenhow, 107 U. S. 769; Poindexter v. Greenhow, 114 U. S. 270. And in Planters' Bank v. Sharp, 6 How. 301, where a bank was chartered with the usual powers to receive money on deposit, discount bills of exchange and notes, and to make loans, and in the course of its business the bank discounted and held promissory notes, and the legislature then passed a law declaring that it should not be lawful for any bank to transfer, by indorsement or otherwise, any note, bill receivable or other evidence of debt, it was held that the statute conflicted with the Constitution and was void. It was said in this case that "a power to dispose of its notes, as well as other property, Opinion of the Court. may well be regarded as an incident to its business as a bank to discount notes, which are required to be in their terms assignable, as well as an incident to its right of holding them and other property, when no express limitation is imposed upon the power to transfer them." In each of the above cases, however, the title to property had either become vested in the grantee by operation of law, or the exercise of the power granted was so far necessary to the full enjoyment of the main object of the charter that persons subscribing to the stock might be presumed to take into consideration, and be influenced in their subscriptions, by the fact that the corporation was endowed with those privileges during the continuance of the charter. 2. Such limitations, however, upon the power of the legislature must be construed in subservience to the general rule that grants by the State are to be construed strictly against the grantees, and that nothing will be presumed to pass except it be expressed in clear and unambiguous language. As was said by Mr. Justice Swayne in Fertilizing Co. v. Hyde Park, 97 U. S. 659, 666: "The rule of construction in this class of cases is that it shall be most strongly against the corporation. Every reasonable doubt is to be resolved adversely. Nothing is to be taken as conceded but what is given in unmistakable terms, or by an implication equally clear. The affirmative must be shown. Silence is negation, and doubt is fatal to the claim. This doctrine is vital to the public welfare. It is axiomatic in the jurisprudence of this court." Hence, an exclusive right to enjoy a certain franchise is never presumed, and unless the charter contain words of exclusion, it is no impairment of the grant to permit another to do the same thing, although the value of the franchise to the first grantee may be wholly destroyed. This principle was laid down at an early day in the case of the Charles River Bridge v. Warren Bridge, 11 Pet. 420, and has been steadily adhered to ever since. Turnpike Company v. The State, 3 Wall. 210; Providence Bank v. Billings, 4 Pet. 514; Pennsylvania Railroad v. Miller, 132 U. S. 75. If however there be an exclusive provision, as, for instance, in the charter of Opinion of the Court. a bridge company that it shall not be lawful for any person to erect another bridge within a certain distance of the bridge authorized, this constitutes an inviolable contract. The Binghampton Bridge, 3 Wall. 51. But even in such cases, if the second charter be for a similar franchise, but to be exercised in a substantially different manner, the exclusive right conferred by the first charter is held not to be violated; as, for instance, if the first charter be for an ordinary bridge, and the second for a railway viaduct, impossible for man or beast to cross, except in railway cars. Bridge Proprietors v. Hoboken Co., 1 Wall. 116. So, if the first franchise be for the sole privilege of supplying a city with water from a designated source, it is not impaired by a grant to another party of the privilege to supply it with water from a different source. Stein v. Bienville Water Supply Co., 141 U. S. 67. Upon a similar principle it was held in Tucker v. Ferguson, 22 Wall. 527, that a tax upon lands owned by a railway company and not used, nor necessary, in working the road and in the exercise of its franchise, was not unlawful, though the charter had provided for a certain tax upon the railroad company, and had enacted that such tax should be in lieu of all other taxes to be imposed within the State. See also West Wisconsin Railway v. Supervisors, 93 U. S. 595. Nor does it follow, from the fact that the contract evidenced by the charter cannot be impaired, that the power of the legislature over such charter is wholly taken away, since statutes which operate only to regulate the manner in which the franchises are to be exercised, and which do not interfere substantially with the enjoyment of the main object of the grant, are not open to the objection of impairing the contract. A familiar instance of this class of legislation is that enacted under what is known as the police power. In virtue of this the State may prescribe regulations contributing to the comfort, safety and health of passengers, the protection of the public at highway crossings or elsewhere, the security of owners of adjacent property, by requiring the track to be fenced, and such appliances to be annexed to the engines as shall prevent the communication of fire to neigh Opinion of the Court boring buildings. Cooley Prin. Const. Law, 321. This power, as was said by Mr. Justice Miller in the Slaughter-house cases, 16 Wall. 36, 62, is and must be, from its very nature, incapable of any very exact definition or limitation. "Upon it depends the security of social order, the life and health of the citizen, the comfort of existence in a thickly populated community, the enjoyment of private and social life, and the beneficial use of property." The following cases show to what extent and for what purposes this power may be exercised: Slaughter-house cases, 16 Wall. 36; Fertilizing Company v. Hyde Park, 97 U. S. 659; Beer Company v. Massachusetts, 97 U. S. 25; Patterson v. Kentucky, 97 U. S. 501; Barbier v. Connolly, 113 U. S. 27; Charlotte, Columbia &c. Railroad v. Gibbes, 142 U. S. 386; Lawton v. Steele, 152 U. S. 133; Eagle Insurance Co. v. Ohio, 153 U. S. 446. And so important is this power and so necessary to the public safety and health, that it cannot be bargained away by the legislature, and hence it has been held that charters for purposes inconsistent with a due regard for the public health or public morals may be abrogated in the interests of a more enlightened public opinion. Stone v. Mississippi, 101 U. S. 814; Phalen v. Virginia, 8 How. 163, 168. In obedience to the same principle it has always been held that the legislature may repeal laws authorizing municipal subscriptions to railways, though such laws were in existence at the time the railway was chartered, and may be supposed to have influenced the promoters and stockholders of the road in undertaking its construction. And even if there has been a public vote in favor of such subscription, such vote does not itself form a contract with the railway company protected by the Constitution, the court holding that until the subscription is actually made the contract is unexecuted. Aspinwall v. Daviess County, 22 How. 364; Wadsworth v. Supervisors, 102 U. S. 534; Norton v. Brownsville, 129 U. S. 479; Concord v. Portsmouth Savings Bank, 92 U. S. 625; Falconer v. Buffalo & Jamestown Railroad, 69 N. Y. 491; Covington & Lexington Railroad v. Kenton County Court, 12 B. Mon. 144; Wilson v. Polk County, 112 Missouri, 126. Opinion of the Court. The contract protected by this clause must also be founded upon a good consideration. If it be a mere nude pact, a bare promise to allow a certain thing to be done, it will be construed as a revocable license. Thus, in Christ Church v. Philadelphia County, 24 How. 300, the legislature of Pennsylvania enacted that the property of Christ Church Hospital, so long as the same should continue to belong to the same hospital, should be and remain free from taxation. In 1851 they enacted that all property then exempted from taxation, other than that which was in the actual use and occupation of such association, should thereafter be subject to taxation. It was held that the original concession of the legislature exempting the property from taxation was spontaneous, and no service or duty or other remunerative consideration was imposed upon the corporation, and hence that it was in the nature of a privilege or license, which might be revoked at the pleasure of the sovereign. In Turnpike Company v. Illinois, 96 U. S. 63, the original charter of the company gave it the right, in consideration of building a turnpike, to erect toll-gates and exact toll for twentyfive years from the date of the charter. In 1861, when the term of charter had more than half expired, the State gave the company a new and additional privilege of using a certain bridge and dyke and of erecting a toll-gate thereon. The only consideration required was that the company should keep them in repair. No term was expressed for the enjoyment of the privileges, and no conditions were imposed for resuming or revoking it on the part of the State. It was held that it could not be presumed to have been intended as a perpetual grant, since the company itself had but a limited period of existence, and that a law resuming possession of the bridge and dyke by subjecting them to the control and management of the city of East St. Louis was not a law impairing the obligation of the contract. In Philadelphia & Grays Ferry Co.'s Appeal, 102 Penn. St. 123, it was also held that a supplement to a charter which merely conferred upon the corporation a new right (as an exclusive right to use and occupy certain streets) or enlarged an |