We have already seen that before banking—as we understand it—was practised in England, moneys were deposited with the goldsmiths for safe keeping only and that in course of time the goldsmiths realised that they were never called upon, at any one time, to repay the whole amount deposited with them; that an undemanded portion always remained in their hands which they could safely use for their own profit. This principle, indeed, constitutes the foundation of modern banking. But the question of what demand _may_ be made on any particular day, or during any given period, has to be considered and provided for by each banker for himself. Experience teaches that on an average over any lengthened period the payments are met in the aggregate, and more than met, by new deposits. This is evidenced by the steady growth of balances held by the banks. The receipts for any one particular day, or during any short period, however, may, and frequently do, fall short of the payments. At the end of each week, for example, bankers lose a large amount of cash, which is drawn for wage-paying purposes, and it is not for several days that this cash gradually dribbles back through tradesmen paying in the money they have received from the wage earners. A similar depletion of cash takes place at the end of each month for the payment of salaries. Again, about the middle of each month suburban and provincial banks have their balances depleted owing to retail customers paying the monthly accounts of their wholesale houses. (This latter demand is not for cash, however, but is satisfied from the Bank of England balances, which, of course, has the same ultimate effect as if actual cash were drawn.) At the end of each quarter there is also a disturbance of balances for rents then falling due; and finally, in the summer and autumn months much actual cash is taken temporarily from the banks for harvest and holiday requirements. Thus the banks lose a portion of their cash or bank balance on certain days and at certain seasons of the year. These demands are all _known demands_, and the banker is prepared accordingly. It is not sufficient, however, that a banker should be in a position to meet _known_ demands; unforeseen demands may be sprung upon him at any moment, and he must be prepared to meet them immediately they arise. Mr. Bagehot, in his _Lombard Street_, writes as follows of these unexpected demands:—