 Its own voluntary act, its own consent, is an element in the transaction.The cases referred to by counsel to the contrary, holding void a consent exacted contrary to the Constitution, have no bearing on these cases.It may, however, be contended (though it is not by the counsel in this case) that the revised charter of 1871 introduced new impositions additional to the mere water rent, such as authorizing a penalty to be imposed by the Board of Public Works, if payment of the water rents were not made by a certain time, and a heavy rate of interest on rents continuing in arrear.