7 PORT ECONOMICS goods, port authorities issue official rate books to intend- ing importers, who are thereby enabled to study the regulations and conditions. RENTALS In addition to rates levied for the general upkeep of the port, and charges made in return for specific services, a port authority will also derive a not inconsiderable income from rentals for the occupancy of space, either in the open as in storage grounds and lumber ponds, or under cover, as in the case of transit sheds and warehouse. It has been pointed out, however, that it is improper to look upon transit sheds as storage depots. But it is legitimate to expect a return from their use for the reception and discharge of cargo. Sheds which are assigned under lease to the continuous use of a firm or company having a line of steamers running to and from the port are said to be “assigned” or “ appropriated,” and the berths to which they belong are styled Appropriated Berths. Other berths and sheds are available for general use as they are requisitioned in accordance with trade requirements. Generally speaking, appropriated berths yield a more substantial return than those which are unappropriated, unless there is a constant and unbroken demand for the latter. Berths are not usually acquired by shipping firms for their individual use unless they can see their way to keep them constantly occupied. It is an advisable procedure, although very rarely practised, for a port authority to keep an analytical return of the user of the berths at the port. In this way, it can be seen whether a berth is remuneratively occupied or not and the causes investigated. This analytical return for purposes of effective comparison can be reduced to terms of expenditure and income per lineal foot or yard of quay frontage, but a certain amount of discrimination will have to be exercised between the various classes of -H