In 1840 a regular mail service by steamers was first introduced on the Atlantic. The first of these mail steamers was the Cunard paddle-steamer _Britannia_, 207 feet long, which sailed from Liverpool on July 4, 1840, and arrived at Halifax in 12 days 10 hours, the return journey being performed in 10 days. The _Acadia_, _Columbia_, and _Caledonia_ all of about the same dimensions as the _Britannia_, at once followed. The success of the Cunard Line was so marked that opposition was soon provoked, and in 1850 the Collins Line of American steamers started to compete with the Cunard liners. The same year also saw the commencement of the well-known Inman Company, of Liverpool, their first vessel being the _City of Glasgow_, an iron screw-steamer of 1680 tons and 350 horse-power. The Allan and Anchor Lines were established in 1856, the Guion Line in 1863, and the White Star Line in 1870. With the substitution of the screw propeller for the paddle wheel, first carried out to any great purpose in the small steamer _Archimedes_ in 1839, but introduced with even greater effect in the Atlantic steamer _Great Britain_ in 1843, was laid the basis of that progressive and magnificent success in propulsion which has since attended ocean navigation. It was with screw-steamers Mr Inman boldly assailed the Cunard Company in 1850, but notwithstanding this, it was only in 1862 that the Government consented to sanction the use of the screw in the mail steamers of the Cunard Company. The _Scotia_, measuring 366 feet in length, by 47½ feet in breadth, and 30½ feet depth, launched in 1861, was the last paddle-steamer built for this company. The other great improvements contributing to the success spoken of, were the introduction of engines designed on the compound principle, and a little later, the employment of the surface condenser, and the use of circular multitubular boilers. In spite of the success with which the compound system was attended in vessels built for the Pacific Steam Navigation Company as early as 1856, and for some other private owners soon after, the great steamship companies, and shipowners generally, were very slow to adopt it. It was not until about the year 1869 that the compound engine came into general use, and it was only in 1872 that the Cunard Company seriously took it into favour.