The power to regulate commerce, vested ln congress, ls the power to preserlbe the rules by which lt shall be governed, that ls, the condltlons upon whlch lt shall be conducted, to determlne when lt shall be free, and when subject to duties or other exactions. Tbe power also embraces within lts control all the instrumentalltles hy which that commerce may be carrled on, and the means by whlch lt may be aided and en-couraged. Gloucester Ferry Co. v. Pennsyl-vania, 114 U. S. 196, 5 Sup. Ct. 826, 29 L. Ed. 158. And see Gibbons v. ogden, 9 wheat. 227, 6 L. Ed. 23 ; Gilman v. Phlladelphla, 3 wall. 724, 18 L. Ed. 96; welton v. Mlssourl. 91 U. S. 279, 23 L. Ed. 347; Leisy v. Hardin, 135 U. S. 100, 10 Sup. Ct 681, 34 L. Ed. 128; Kavanaugh v. Southern R. Co., 120 Ga. 62, 47 S. E. 526