When this resource is exhausted, and it becomes necessary, in order to raise money, to assign or mortgage some particular branch of the public revenue for the payment of the debt, government has, upon different occasions, done this in two different ways. Sometimes it has made this assignment or mortgage for a short period of time only, a year, or a few years, for example; and sometimes for perpetuity. In the one case, the fund was supposed sufficient to pay, within the limited time, both principal and interest of the money borrowed. In the other, it was supposed sufficient to pay the interest only, or a perpetual annuity equivalent to the interest, government being at liberty to redeem, at any time, this annuity, upon paying back the principal sum borrowed. When money was raised in the one way, it was said to be raised by anticipation; when in the other, by perpetual funding, or, more shortly, by funding.