All of these authorities agree that the application of a given power produces about the same effect, whether through the side-wheel or the screw; and if so, it is evident that the screw can not attain the same speed as the side-wheel, without burning as much fuel, and having as costly and as heavy engines and boilers. Indeed, taking the whole evidence together, it appears well settled by these authorities, that the screw is equal to the side-wheel only in smooth water, and that, as a consequence of this distinction, it is not equal to it in general ocean navigation. It has been seen that much of its power is lost when it contends with head-winds and seas, and that when it has attained a fair average mail speed, the wind will help it very little, if any, under the most favorable circumstances. It is, therefore, reasonable to infer that it would cost more to attain a high average mail speed with the propeller than with the side-wheel. If in attaining this average mail speed the advantages are clearly in favor of the side-wheel, there is no hope that we shall accomplish the mail service at cheaper rates than heretofore, as this agency can not be introduced toward that end; for not only is the prime cost of the steamer the same, as also the consumption of fuel per mile, but there are other and numerous disadvantages connected with the propeller, which are wholly unknown to the side-wheel. It is a well-known fact that propellers are compelled to be placed upon the docks three or four times as often as side-wheels. The screw either breaks, and must be replaced by another, or it cuts the boxes out, or works the stern of the vessel to pieces. Any one of these requires that the steamer shall be docked, however great the expense; and as these accidents are constantly occurring in even the best constructed and best regulated propellers, it follows that they must be constantly on the docks. This species of vessel being built necessarily narrower than the side-wheel, it rolls more, and is found to be an exceedingly disagreeable passenger vessel. Propellers have become deservedly unpopular the world over; and if it were possible for them to be faster than the side-wheel, it is hardly probable that first-class passengers would even then go by them, as they are known to be so exceedingly uncomfortable.