The Act is, as its name implies, concerned with the "acquisition" of land by the Commonwealth. The power of acquisition which it confers is a power to "acquire land for a public purpose" (s. 6). As a matter of language, a power to acquire land for a public purpose appears to us to be prima facie limited to an acquisition of land which is needed or which it is proposed to use, apply or preserve for the advancement or achievement of that purpose: see, generally, Attorney-General (Cth) v. Schmidt [1] and Halsbury's Laws of England, 4th ed., vol. 8, par. 50. Adapting words used in this Court in a different context, the "purpose of which [s. 6] speaks" is "the use to which" the land acquired is "to be put": see, as regards s. 26(a) of the Income Tax Assessment Act 1936 Cth, per Rich, Dixon and Evatt JJ., Evans v. Deputy Federal Commissioner of Taxation (S.A.) [2] and per Fullagar J., Pascoe v. Federal Commissioner of Taxation [3] . That view of the nature of the power conferred by the Act derives support from other provisions in it. Thus the long title, to which resort may properly be had in case of ambiguity for guidance on the intended scope of the Act (see, per Latham C.J., Birch v. Allen [4] ), describes the Act as an Act "to make provision for the Acquisition by the Commonwealth of Land required for Public Purposes " (emphasis added). Again, when the Act comes, in Pt III, to authorize preliminary or ancillary steps in relation to a proposed acquisition, such as the obtaining of information in relation to the relevant land, it confines the authorization to acts which are "for the purpose of ascertaining whether [the] land is suitable for a public purpose or of surveying or obtaining information in relation to [the] land which [the person authorized] considers suitable for such a purpose" (s. 16(1)) (emphasis added). On that prima facie construction, the provisions of the Act would fall short of enabling the Commonwealth compulsorily to acquire land in circumstances where it is not suggested that the Commonwealth's purpose relates to any planned use, application or preservation of the land itself or of any buildings thereon but is for the purpose of depriving the owner of his possession of the land with the motive of thereby achieving some consequential advantage which can properly be described as a "public purpose": cf. Jones v. The Commonwealth [5] .