The form of legislation adopted in the Air Navigation Act 1920 is within the powers and discretion of the Commonwealth Parliament (Roche v. Kronheimer[34]; Victorian Stevedoring and General Contracting Co. Pty. Ltd. and Meakes v. Dignan[35]). But is the Act a law with respect to external affairs? The Constitution, in the legislative power to make laws with respect to external affairs, recognizes that the Commonwealth will have political relations with other Powers and States, and legislative power is conferred upon it in comprehensive terms, so that it may control those foreign or external relations, and implement obligations that may have been assumed in the course of those relations. Again, this fact is recognized in the jurisdiction conferred by the Constitution, sec. 75, upon the High Court in all matters arising under any treaty or affecting consuls or other representatives of other countries. The Air Navigation Act enables the Governor-General to carry out and give effect to a convention made with other Powers and States. The convention for the regulation of aerial navigation concerns the relations of those Powers and States with Australia, and the intercourse of their nationals with Australia's nationals by means of aerial navigation. Its stipulations recognize the sovereignty of every State in the air space above its territories, and control and regulate the rights and obligations of the contracting Powers and States, and their nationals, in respect of the use of the air superincumbent on those territories. The convention is made with Powers and States external to Australia, and involves international obligations. But what else are external affairs of a State - or, to use the more common expression, the foreign affairs or foreign relations of a State - but matters which concern its relations and intercourse with other Powers or States and the consequent rights and obligations? The power conferred by the Constitution upon the Commonwealth to make laws with respect to external affairs must be exercised with regard to the various constitutional limitations expressed or implied in the Constitution, which restrain generally the exercise of Federal powers. The Commonwealth cannot do what the Constitution forbids. But otherwise the power is comprehensive in terms and must be commensurate with the obligations that the Commonwealth may properly assume in its relations with other Powers or States. It is impossible, I think, to define more accurately, at the present time, the precise limits of the power. It may be, as Willoughby suggests in connection with the treaty-making power in the Constitution of the United States, that the laws will be within power only if the matter is "of sufficient international significance to make it a legitimate subject for international co-operation and agreement" (Willoughby on The Constitutional Law of the United States, 2nd ed. (1929), p. 519). While neither the Constitution of the United States nor the British North America Act is a very safe guide to the construction of the Constitution Act of Australia, the decisions under those Acts are not opposed to the construction of the Australian Constitution that I adopt (See Missouri v. Holland[36] and the Aeronautics Case[37]). However the limits of the external affairs power may hereafter be defined or restricted, that power does, in my judgment, authorize the Parliament to confer upon the Governor-General power to make laws to carry out and give effect to the aerial navigation convention of 1919, because that convention recognizes sovereignty of the contracting parties in the air space above their territories, confers rights upon Australia and her citizens and assumes obligations in respect of the air space above Australia towards foreign powers or States and their nationals. A law providing for the carrying out and giving effect to an international convention of this character concerns Australia's relations and intercourse with other Powers or States and the rights and obligations which result, and is thus a law for the peace, order and good government of the Commonwealth with respect to external affairs.