If the large class of steamers can not live on their own receipts, much less can the small. An adequate speed for the mails leaves no available space for cargo. The ship may carry two or three hundred tons of freight; but it pays perhaps but little more than the handling and the extra coal necessary to transport its extra weight. As a general thing, it may be safely said that when a vessel is well adapted to the mails and passengers she is filled with her own power, that is, with heavy engines, large boilers, and a large quantity of fuel, as also with her provisions and baggage. We have already seen how the size and weight of engines and boilers must increase, as well as the bulk and cost of the fuel, to gain a little speed. But it is not generally known how large a quantity of consumable stores and baggage go in a well-supported mail packet. The greater the postal efficiency of a steamer the less is it able to carry freight; and the time will doubtless soon come when the fast mail packets will take nothing except a few express packages. The Persia now takes scarcely any freight, and the Vanderbilt can not think of doing it when she makes fast trips. It is very probable that the whole system of the ocean will be materially changed; and that while clippers and slow propellers carry the fine freights, fast vessels filled with their own power will carry the mails and passengers. And in doing this, they can not, of course, support themselves; neither will they conflict with private enterprise in freight transport. It is now the case to a large extent on most of our American lines.