We have now been able to see steamship lines established and sending their fleets regularly with passengers, cargoes, and mails to the uttermost ends of the earth, and we have been able to look ahead a little so that we shall be free to concentrate our attention very shortly on that centre of steamship activity the North Atlantic. Between 1840 and 1860 the Cunard Company had practically a monopoly of the Atlantic trade. For a time the American clippers hung on, but as they had ousted the old brigs, even the fastest sailing vessels were replaced by the steamship. From 1850 to 1858 there was, indeed, some opposition from a steamship company called the Collins Line, which had been subsidised by the American Government. This competition was very keen, for both lines were compelled to put forth the best steamers they could, but in the end the Collins Line withdrew from the contest. [Illustration: DESIGNS FOR SCREW PROPELLERS PRIOR TO 1850. _From the Drawing in the Victoria and Albert Museum._] But there was now another force coming in, which was to entirely alter the character of the liner. Let us trace the evolution of the screw propeller, which has completely banished the old-fashioned paddle-wheel from its place in the ocean-going ship, and is rapidly having the same effect in cross-Channel steamers. We saw that away back in 1804 John Stevens had crossed the Hudson in a little ship that was driven along by a screw propeller, but it was not until the year 1836 that the screw was re-introduced. In this year John Ericsson, a Swedish engineer, obtained a patent for his invention which consisted of two drums, on whose exteriors were seven helical blades, the interior of each drum having the three blades which formed the radii of the circle. Both these drums worked on one axis, and were placed behind the rudder, and not in front of it as is the modern propeller. If the reader will turn to the plate facing page 118, he will see this at the beginning of the second line to the left. The drums were made to work in opposite directions, the object being to avoid loss due to the rotary motion already remaining in the water discharged by a single screw.