It shall be lawful for the Committee of Management of the Invercagill Athenaeum by deed under their corporate seal with the sanction and consent of the Superintendent to lease from time to time at such rent and on such conditions as they may think reasonable the whole or any part of the parcel of land specified in the Schedule annexed to the said Invercagill Athenaeum Reserve Management Ordinance 1871 not required for the purposes of the said Institution for any term or terms of years not exceeding 21 years at any one time.