But the grant which has been made to the president and trustees of Bowdoin college, out of the tax laid upon the banks within this commonwealth, shall be charged upon the tax upon the banks within the said district of Maine, and paid according to the terms of said grant; and the president and trustees, and the overseers of said college, shall have, hold and enjoy their powers and privileges in all respects; so that the same shall not be subject to be altered, limited, annulled or restrained except by judicial process, according to the principles of law; and in all grants hereafter to be made, by either state, of unlocated land within the said district, the same reservations shall be made for the benefit of schools and of the ministry, as have heretofore been usual, in grants made by this commonwealth.