Much trouble was caused by the injurious effects of bilge-water and foul air in the holds of ships, and various remedies were devised from time to time. In 1715 structural improvements were devised to allow of the bilge-water flowing more freely to the pumps, and trunks were fitted to the lower decks to convey air to the holds. In 1719 it was proposed that the holds of ships should have several feet of water run into them in the early spring in order to cool them, and that it should not be pumped out till August; but this remedy was never extensively practised. In 1753 Dr. S. Hales proposed a system of ventilation by means of windmills and hand-pumps, which produced excellent results. It was noticed that the accumulation of carbonic acid gas and foul damp air in the holds, not only set up rapid decay in the ship, but also most injuriously affected the health of the crews. Dr. Hales' system was employed in the _Prince_ from 1753 to 1798, and it was considered that the durability of this vessel had been greatly increased. It was also reported by Lord Halifax that the mortality on the non-ventilated ships on the coast of Nova Scotia was twelve times as great as on those vessels which were fitted with Dr. Hales' appliances. There are not many records in existence of the merchant-vessels of this period. Fig. 54 is a representation of an armed East Indiaman which was launched at Blackwall in 1752. Her length of keel was 108 ft. 9 in.; breadth, 34 ft.; and burthen, 668 tons. She was named the _Falmouth_, and was constructed by the famous shipbuilder, John Perry, of Blackwall Yard. She was commenced almost exactly two years before the date of her launch. Like all her class, she was heavily armed. [Illustration: FIG. 54.--The _Falmouth_. East Indiaman. Launched 1752.]