upon the face of the statute, the court can see no possible relation to the public health or safety, or, possibly, general welfare, it will hold the law null in so far as it invades either property or liberty rights because not under the police power.  If, on the other hand, they can see some relation to the public health, safety, or general welfare, even though they do not think it the best method of bringing about the desired result, they will not presume to run counter to legislative opinion.  Of the expediency of the statute, the legislature must be and is the final judge.

With us the police power is exercised largely for moral reasons.  That is to say, the great instances of its extension have been connected with moral or sanitary reform.  No doubt the police power may broaden with advancing civilization and more complex appliances and possibly greater medical knowledge and social solidarity.  No doubt purposes which were once lawful may be unlawful, and property devoted to them thus be destroyed by a change in the law.  Mr. Justice Brewer, of our Supreme Court, holding the contrary view, was overruled by the majority, and that decision is final.[1] Not only we, but a State, may not even make a contract which shall be immune from future extension of the police power, the Dartmouth College case notwithstanding.  For instance, the State of Massachusetts in 1827 granted a perpetual franchise to a corporation to make beer.  It was allowed, forty years later, to pass a law that no corporation should make beer, and the brewery became valueless.  The State of Minnesota granted a perpetual franchise to a railroad to fix its own fares.  Twenty years later it took away that right, thereby, as claimed, making the railroad property valueless; the railroad had no remedy.  A man in Connecticut had barrels of whiskey in a cellar for many years, but the State was allowed to pass a law prohibiting its sale; which, of course, had he been a teetotaler, would have deprived that property of all value, and in any case, of all exchange value.  A man in Iowa owns one glass of whiskey for several years, and then a law is passed forbidding him to sell it; the law is valid.  A youth in Nebraska buys tobacco and paper and rolls a cigarette.  The State afterward passes a law forbidding smoking by minors.  It is a crime if he light it.  Sufficient has, perhaps, been said to show the extraordinary scope and elasticity of this, the widest, vaguest, and most dangerous domain of our modern legislation, though perhaps we should add one or two striking cases affecting personal liberty, as, for instance, a citizen of Pennsylvania marries his first cousin in Delaware and returns to Pennsylvania, where the marriage is void and he becomes guilty of a criminal offence; a white man in Massachusetts who marries a negress or mulatto may be guilty of the crime of miscegenation in other States; a woman might work fifty-eight hours a week in Rhode Island, but if she work over fifty-six in Massachusetts may involve her employer, as well as herself, in a penal offence.