_First_, as to public conveyances on land and water. In _New Jersey Steam Navigation Co. ~v.~ Merchants’ Bank_, 6 How. 344, this court, speaking by Mr. Justice Nelson, said that a common carrier is “in the exercise of a sort of public office, and has public duties to perform, from which he should not be permitted to exonerate himself without the assent of the parties concerned.” To the same effect is _Munn ~v.~ Illinois_, 94 U. S. 113. In _Olcott ~v.~ Supervisors_, 16 Wall. 678, it was ruled that railroads are public highways, established by authority of the State for public use; that they are none the less public highways, because controlled and owned by private corporations; that it is a part of the function of government to make and maintain highways for the convenience of the public; that no matter who is the agent, or what is the agency, the function performed is _that of the State_; that although the owners may be private companies, they may be compelled to permit the public to use these works in the manner in which they can be used; that, upon these grounds alone, have the courts sustained the investiture of railroad corporations with the State’s right of eminent domain, or the right of municipal corporations, under legislative authority, to assess, levy and collect taxes to aid in the construction of railroads. So in _Township of Queensbury ~v.~ Culver_, 19 Wall. 83, it was said that a municipal subscription of railroad stock was in aid of the construction and maintenance of a public highway, and for the promotion of a public use. Again, in _Township of Pine Grove ~v.~ Talcott_, 19 Wall. 666: “Though the corporation [railroad] was private, its work was public, as much so as if it were to be constructed by the State.” To the like effect are numerous adjudications in this and the State courts with which the profession is familiar, The Supreme Judicial Court of Massachusetts, in _Inhabitants of Worcester ~v.~ The Western R. R. Corporation_, 4 Met. 564, said in reference to a railroad: