Although we have not deemed it necessary in the present paper to touch on the national struggle between steam-ships, we must not forget that one of the most promising and valuable features in steam navigation arose as an appendage to sailing. The _auxiliary screw_ will deserve the blessings of our colonists, for reasons which may be soon told. When it was yet uncertain what result would mark the contest _Screw_ v. _Paddle_, it was suggested that the screw-propeller might probably be used as an auxiliary power, for occasional use during calms and contrary winds; the vessel to be a sailing-vessel under ordinary circumstances; but to have a marine engine and a screw for exigencies at times when the ship would be brought to a stand-still or even driven backwards. About seven years ago, an American packet-ship, the _Massachusetts_, a complete sailing-vessel in other respects, was provided with a screw and a steam-engine powerful enough to keep the ship moving when winds and tides were adverse; the screw was capable of being lifted out of the water when not in use. In her first voyage from Liverpool to America, this ship gained from five to thirteen days as compared with five other ships which sailed either on the same or the following day. This experiment was deemed so far successful, that the Admiralty ordered, in 1846, an auxiliary screw to be fitted to the _Amphion_ frigate, then building at Woolwich. Another example was the _Sarah Sands_, an iron ship of 1300 tons; she had engines of 180 horse-power, much below that requisite for an ordinary steamer of the same size. She could carry three classes of passengers, coal for the whole voyage, and 900 tons of merchandise. She made four voyages in 1847, two out and two home; and in 1848 she made five: her average time was about nineteen days out, and seventeen days home, and she usually passed about six liners on the voyage. The speed here mentioned is not quite equal to that of the truly remarkable clippers noticed above, but it far exceeded that of any liner at work in 1848. The example was followed in other vessels; and then men began to cherish the vision of a propeller screwing its way through the broad ocean to our distant colonies. From this humble beginning as an auxiliary, the screw has obtained a place of more and more dignity, until at length we see the mails for the Cape and for Australia intrusted confidently to its safe-keeping. The icy regions of the north are braved by the auxiliary screw. The little _Isabel_, fitted out almost entirely at the expense of Lady Franklin to aid in the search for her gallant husband, is a brigantine of 180 tons, with an auxiliary screw to ship and unship. The _Intrepid_ and the _Pioneer_, the two screw-steamers which form part of Sir Edward Belcher's arctic expedition--lately started from England--are to work with or without their auxiliary appendage as circumstances may determine.