As the adaptability of iron for constructional purposes became more generally recognised, it led to the proposal that steamers should be built on the longitudinal principle instead of with an ordinary keel and a series of transverse ribs. The use of iron also enabled shipbuilders to increase the safety of their vessels considerably by means of transverse bulkheads, the number of these being increased until, even as early as 1838, the iron steamers then being built for the Glasgow and Liverpool line were each divided into five sections, any three of which were estimated to be sufficient to keep the steamer afloat if the other two should become waterlogged through collision. Several vessels were constructed on modifications of the longitudinal system, the chief among them being the _Great Eastern_. In 1853 James Hodgson of Liverpool issued a circular on the advantages of iron sailing ships, in which he pointed out not only the greater strength obtained by using iron but the comparative cheapness of construction. The circular stated that a wooden ship of 1000 tons would cost £16 10_s._ per ton, and an iron ship £13 10_s._ per ton, both fitted for trade to the East. The wooden ship would not carry more than 1500 tons, whereas an iron ship built from the same external lines would carry 1800 tons, and this difference at £5 per ton out and home, added to allowances for insurance, depreciation, and interest, would make a difference in favour of the iron ship of £2295. [Illustration: THE “SARAH SANDS,” 1846.] What was true of sailing ships was equally true of steamers, and Hodgson had shown this some years before the publication of his circular, when he built the _Sarah Sands_.