What I have called the secondary aspect of the defence power has so far only been invoked and expounded in connection with an actual state of war in which Australia has been involved. It has hitherto, I think, been treated in the cases as coming into existence upon the commencement or immediate apprehension of war and continuing during war and the period necessary for post-war readjustment. In a world of uncertain and rapidly changing international situations it may well be held to arise in some degree upon circumstances which fall short of an immediate apprehension of war. In its secondary aspect the power extends to an infinite variety of matters which could not be regarded in the normal conditions of national life as having any connection with defence. Examples now familiar are the prices of goods and the rationing of goods, rents and the eviction of tenants, the transfer of interests in land, and the conditions of employment in industry generally. It may be that, on its true analysis, this secondary aspect of the defence power depends wholly on s. 51 (xxxix.) of the Constitution. On this view, the effect of a national emergency is that the matters which I have mentioned, and very many others, become "matters incidental to the execution" of the power of the Executive to deal with the emergency. Having in mind this secondary or extended aspect of the power, Dixon J., in Andrews v. Howell [1] , said of the power given by s. 51 (vi.): - "Though its meaning does not change, yet, unlike some other powers, its application depends upon facts, and, as those facts change, so may its actual operation as a power enabling the legislature to make a particular law. The existence and character of hostilities, or a threat of hostilities, against the Commonwealth are facts which will determine the extent of the operation of the power." Other passages to a similar effect could be cited. In such passages the "facts" referred to are the basic facts which give rise to the extension of the power. Such facts have always hitherto been matters of public general knowledge, and matters, therefore, of which a court can and will take judicial notice. But, given the basic fact of (say) war, the question will still arise, whenever the validity of a particular law is in question, whether that law can be related to the extended power, or whether it is a law with respect to a matter incidental to the power of the Executive to wage war. The matter is, in effect, taken in two stages. At the first stage, the existence of war or national emergency is recognized as bringing into play the secondary or extended aspect of the defence power. This is done simply as a matter of judicial notice, and it provides the justification for a presumption of validity which might not otherwise exist in the case of an enactment which on its face bore no relation to any constitutional power. At the second stage the enactment in question is examined with regard to its character as a step to assist in dealing with the emergency, and "the presumption is, so to speak, reinforced by the respect which the court pays to the opinion or judgment of the other organs of government, with whom the responsibility for carrying on the war rests. When, for example, it appears that a challenged regulation is a means adopted to secure some end relating to the prosecution of the war, the court does not substitute for that of the Executive its own opinion of the appropriateness or sufficiency of the means to promote the desired end" (per Dixon J. in Stenhouse v. Coleman [2] ). The question which arises at this second stage may itself turn on particular facts as distinct from the overriding general fact of war or national emergency. Such facts may relate to the operation of the law in question or to a state of affairs which calls for its enactment. Whether any and what evidence of such facts is admissible must depend on the circumstances of each particular case. In Jenkins v. The Commonwealth [1] , and in Sloan v. Pollard [2] , evidence was admitted. On the other hand, affidavits were rejected in the Uniform Tax Case [3] and in R. v. Foster; Ex parte Rural Bank of New South Wales [4] , the Court in each case confining itself to matters of which judicial notice could be taken. The Court will normally, I think, so confine itself. In Stenhouse v. Coleman [5] Dixon J. said: - "Ordinarily the Court does not go beyond matters of which it may take judicial notice. This means that for its facts the court must depend upon matters of general public knowledge." The reasons why this must generally be so are stated in his Honour's judgment. The taking of evidence might often involve disclosures which would be prejudicial to the steps being taken by the Executive to deal with the emergency. The Court, in any case, is bound by the legal rules of evidence, and there are thus limitations upon the material which it can receive or take into account. It may perhaps be added that the "facts" will in many cases be of such a general character as to be difficult or impossible to prove or disprove by legally admissible evidence, while quite capable of being judicially noticed. It is indeed a characteristic of a large class of matters which are judicially noticed that they are of this general character. In Holland v. Jones [6] , Isaacs J. said: - "Wherever a fact is so generally known that every ordinary person may be reasonably presumed to be aware of it, the Court "notices" it, either simpliciter if it is at once satisfied of the fact without more, or after such information or investigation as it considers reliable and necessary in order to eliminate any reasonable doubt. The basic essential is that the fact is to be of a class that is so generally known as to give rise to the presumption that all persons are aware of it. This excludes from the operation of judicial notice what are not "general" but "particular" facts. But, if the fact is of such "general" character as to give rise to the presumption mentioned, then a Judge is justified in "noticing" it."