delivered the opinion of the Court:

Counsel for the plaintiff in error claim that the court below erred in not directing a verdict for the defendant in each case, upon the ground that the law upon which the informations were based was unconstitutional, and also that the court erred in striking out the evidence of the defendant introduced and proffered, as we have just stated; and also in deciding that the question whether or not such evidence constituted an “extraordinary emergency” was not a question of fact to be determined by the jury only.

First. These prosecutions in the court below were based upon the following sections of the District Code:

“Sec. 892. Limitation Of flours Of Daily Service For Laborers And Mechanics On Public Works. — The service and employment of all laborers and mechanics who are now, or may hereafter be, employed by the government of the United States, by the District of Columbia, or by any contractor or subcontractor upon any of the public works of the United States or of *457tbe said District of Columbia, is hereby limited and restricted to eight hours in any one calendar day; and it shall be unlawful for any officer of the United States government or of the District of Columbia, or any such contractor or subcontractor, whose duty it shall be to employ, direct, or control the service of such laborers or mechanics, to require or permit any such laborer or mechanic to work more than eight hours in any calendar day, except in case of extraordinary emergency.

“Sec. 893. Any officer or agent of the government of the United States or of the District of Columbia, or any contractor or subcontractor, whose duty it shall be to employ, direct, or control any laborer or mechanic employed upon any of the public works of the United States or of the District of Columbia, who shall intentionally violate any provision of the last preceding section, for each and every such offense shall be punished by a fine not to exceed $1,000, or by imprisonment for not more than six months, or both.” [31 Stat. at L. 1334, chap. 854.]

In Atkin v. Kansas, 191 U. S. 207, 48 L. ed. 148, 24 Sup. Ct. Rep. 124, where a similar statute of the State of Kansas was upheld, the Supreme Court has in effect decided that the District statute we here consider is constitutional. The service and employment of Shillingberg and his eoworkers by the plaintiff in error, a contractor with the District of Columbia, upon this public work of the District of Columbia, was by this statute limited and restricted to eight hours in any one calendar day; and it was unlawful for this contractor to require or permit Schilling-berg to work more than eight hours in any one calendar day, except in case of extraordinary emergency; and if the plaintiff in error violated this provision, for each and every such offense he became liable to be punished by a fine or by imprisonment, or both, as provided by this statute. The government of the District of Columbia is simply an agency of the United States for-conducting the affairs of its government in the Federal District, and this work on the Piney Branch creek bridge was of a public,, and not of a private, character. As the Supreme Court has said, in effect, there is no possible ground to dispute the power of Congress to declare that no one undertaking work for the District *458of Columbia should permit or require an employee on such work to labor more than eight hours in any one calendar day, and to inflict punishment upon those coming within the law and disregarding it. To prohibit a contractor from doing public work for the District in his own way and in his own time, without regard to the will of Congress, does not infringe upon his liberty. Congress may lawfully prescribe the conditions upon which it will permit public work in this District to be done in its behalf; and by this statute Congress appears to have determined that to restrict a day’s work to eight hours tends to promote morality, to improve the physical and intellectual condition of working men, and to enable them to better discharge their duties as citizens of the Republic. It is not in derogation of the liberty of either employee or employer, to make it a criminal offense for this contractor for this public work to permit or require his employees to work more than eight hours in one calendar day. No employee has an absolute right to perform labor for the State, and no contractor for a public work can excuse a violation of his agreement with the government by doing anything which under the statute, made part of its contract, he is distinctly forbidden to do. The plaintiff in error is not by such a statute denied the equal protection of the law, for this statute prescribes a rule of conduct which applies alike to all who contract to do work for the District of Columbia, and alike to all employed to perform labor on such a work, and Congress has the right to prescribe the conditions under which it will permit work of this kind to be done for the District of Columbia. By this law it has done so, and in so doing has not infringed the personal rights of either employers or employees upon such public work. The Nnited States in this Federal District’may dictate the terms and conditions of the contracts this District may make, and it may prescribe the hours of labor to be observed by its contractors and their employees on its public works. See Atkin v. Kansas (supra); United States v. Martin, 94 U. S. 400, 24 L. ed. 128; United States v. Driscoll, 96 U. S. 421, 24 L. ed. 847; and United States v. San Francisco Bridge Co. 88 Fed. 891.

Second. The court below committed no error .in. excluding *459from the consideration of the jury the testimony introduced and •proffered by the defendant to show that in this case an “extraordinary emergency” had happened, within the meaning of this statute. It was the duty of the court to determine, what jurors ■unguided could not settle for themselves, what would amount to an “extraordinary emergency.” This question was one of statutory construction for the court. It was for the court to say whether all the evidence admitted and proffered tended in this case to prove the existence of an “extraordinary emergency.” The court here rightly decided that such evidence did not tend to prove its existence. In this statute the term “extraordinary emergency” imports a sudden and unexpected happening; an unforeseen occurrence or condition calling for immediate action to avert imminent danger to health, or life, or property; an unusual peril, actual, and not imaginary, suddenly creating a situation so different from the usual or ordinary course in the prosecution of the public work that the court may and must conclude that Congress contemplated excepting from the operation of this law such an occurrence, so sudden, rare, and unforeseen. In the case before us the District and the contractor should know that concrete in an arch may not harden in a given part of eight hours; and, since the contract permitted the District engineers to make changes in the plan, the contractor might have contemplated that the excavation would need greater depth to support the arch of the bridge than an earlier examination, had shown likely to be required. The evidence relied upon by the defendant would not have justified the jury in concluding that either or both of these circumstances constituted an extraordinary emergency. The court could have so instructed the jury, and it therefore committed no reversible error in excluding all this evidence from the consideration of the jury, since it was offered only to prove an extraordinary emergency, and it did not tend to prove it. See United States v. Ellis, U. S. Dist. Ct. Mass. [affirmed in 206 U. S. 246, 51 L. ed. —, 27 Sup. Ct. Rep. 600]; United States v. Sheridan-Kirk Contract Co. 149 Fed. 813; and Sparf v. United States, 156 U. S. 51, 103, 39 L. ed. 343, 361, 15 Sup. Ct. Rep. 273.

*460Tbe third assignment of error, namely, that tbe court erred in bolding that wbat constituted an extraordinary emergency was not a question of fact for tbe jury, we bave sufficiently discussed in wbat we bave said.

Tbe court below committed no reversible error, and tbe judgment must be affirmed, and it is so ordered.