The river trials of the _Rattler_ lasted from October 1843 to the beginning of 1845, and showed that the screw-shaft might be advantageously reduced in diameter, and the blades by about one-third of their length, an alteration which greatly reduced the weight of the screw, and facilitated the operation of shipping and unshipping it, while rendering unnecessary the wounding to so great an extent of the after part of the vessel. Before, however, this last point was decided (it not being evident that the good performance of the shorter screw was not attributable to the greater clearance which the reduction of its length had caused), the screw aperture was partly filled up in a temporary manner, so as to leave the shorter screw the same clearance as the longer one had originally. The result of this experiment proved that the aperture in future vessels might be constructed of very moderate dimensions without lessening the propelling power of the screw. [Sidenote: The _Rattler_ not as successful as expected.] These trials clearly showed that the screw, as an instrument of propulsion in smooth water, is not inferior to the paddle-wheel. But further experiments were considered necessary to establish its superiority in all respects. In the early part of the year 1845 the _Rattler_ proceeded, in company with the _Victoria and Albert_ and the _Black Eagle_, from Portsmouth to Pembroke. When rounding the Land’s End, and steaming against a strong head wind, both these vessels, as might be expected, showed a great superiority, their power being much greater than the _Rattler’s_ in proportion to the resistance, and their paddle-floats being constructed on the feathering principle. This comparative failure of the _Rattler_ left an unfavourable impression as to the efficiency of the screw against wind and sea in heavy weather, and this impression continued for several years, although when next tried in a run from the Thames to Leith, she showed in respect to speed a decided superiority over one of the paddle-wheel vessels employed in that trade, whose power as compared with her tonnage was greater than that of her competitor. Before joining the squadron under the command of Rear-Admiral Hyde Parker in July 1845, the _Rattler_ was employed to tow the _Erebus_ and _Terror_ to the Orkney Islands on their fatal expedition to the North Pole, and she seems to have performed that duty to the entire satisfaction of Sir John Franklin. [Sidenote: Captain Robert F. Stockton efficiently supports Ericsson’s views.]