But with all these advantages, a considerable time elapsed before the Admiralty could be induced to consider the desirability of constructing any Government steamer of iron, or of even allowing the large private trading vessels engaged in the conveyance of the mails to be built of that material. They had objections of their own applying specially to the ships under their control, and very plausible objections too, in their opinion, compared with those originally raised by an ignorant public. A shot, they said, would penetrate an iron vessel with much greater ease than a wooden one, while the shot holes could not be as effectually plugged, if indeed they could be plugged at all. Wood, they argued, when pierced, would rapidly contract and leave a very small opening for water to get through, whereas a shot would make a clean cut through an iron plate which could not be thus expeditiously filled, and if it did not tear away the whole of the plate, would leave a gap as large as a “barn door.” However, a little experience[124] soon showed their arguments to be fallacious, and when they found that the engines of a paddle-wheel steamer, and, especially, the paddles themselves, offered conspicuous targets to an enemy, and that it was impossible to make the stern-frames of their wooden ships sufficiently strong to withstand, without serious leakage, the vibration of the screw, they abandoned, though reluctantly, the paddle-wheel, and at length gave up, also, vessels of wood for the purposes of war. These resolutions were, however, only carried into practice after vast sums of money had been expended on the “reconstruction” of a _wooden_ British Navy, for which, in one year alone, and that so lately as 1861, when almost everybody except themselves saw that iron must supersede timber, they demanded from Parliament (and carried their vote) no less than 949,371_l._ to replenish the stock of wood in the dockyards: a sum far in excess of any previous vote for that material.[125] [Sidenote: Mr. Galloway’s feathering paddles, 1829.] [Illustration] While the art of steam navigation made rapid progress, the ingenuity of engineers had been constantly directed to the improvement of the paddle-wheels; and the above drawing of one, with “feathering paddles,” patented by Mr. Galloway in 1829,[126] represents the most perfect of any wheel in use at that period, and has not been materially improved on since then. But, at that time also, a substitute for the paddle was seeking practical solution. The screw, as a means of propulsion, had been suggested long before the steamboat had been brought into use. Indeed, its principle was known at a very early period in the use of an oar for sculling, and could, as already explained, be seen in the movements of the tail of a fish. [Sidenote: Story of the screw-propeller.]