It thus appears that with any appreciable economy the propeller must be slower than the side-wheel; and that with any considerable economy it can be but little faster than sail. It has, however, the advantage over sail of being rather more reliable and punctual, and can make arrivals and departures rather more matters of certainty. This at the same time secures to it a better class of freights as well as vast numbers of emigrants which together, enable it to incur the extra expense over a sailing vessel. The cargo is less in the propeller than in the sail, as much of the room is occupied by the engines, boilers, and fuel. Hence, the prices must be proportionally higher to meet the deficit arising from the smaller quantity. But there are very few trades in which propellers can run as noticed on so long a voyage as 3,000 to 4,000 miles; and these lie between a few countries in Europe and the ports of the United States. Their support arises chiefly from the emigrant trade; as without this their freights would not on any known lines enable them to run one month. And this is not simply an assumption of theory, but the experience of all the European lines. I was recently told in England and France by many persons who had no interest or desire to deceive me, that propeller stock was invariably a burthen to every body having any thing to do with it, and could generally be bought at sixty to seventy cents on the dollar, while much of it would not bring half of its cost price. They cited as an evidence the fact that no line of propellers is permanent, unless in some way connected with a subsidized company, as in the case of the Cunard screws running between Liverpool and New-York. The Glasgow line is also an exception, and is said to pay dividends. The screw lines are always hunting a home and a new trade. (_See views of Mr. Murray, page 111._)