Many highly-improved methods of ventilation are now open to the shipowner; the number of patented systems in use or awaiting adoption being adequate testimony to the widespread attention bestowed upon the subject. These divide themselves into two general classes:—firstly, systems which aim at providing an efficient self-acting series of ventilating pipes in which the natural current or that induced by the vessel’s own speed through the atmosphere, is the only force utilised; and secondly, those in which machines driven by steam power are employed to produce fresh currents or extract vitiated atmosphere. [Illustration: FIG. 12.] [Illustration: FIG. 13.] Various forms of ventilators, belonging to the first-named class, have been introduced into many ocean-going passenger vessels within recent years, the result being a considerable improvement in the sanitary condition of the more confined portions of vessels. One of the most approved of these, receiving specially extended adoption, amounting as it does to a highly perfected system, may be noticed a little in detail. This is the form of ventilator patented and introduced by Messrs R. Boyle & Son, the well known ventilating engineers of London and Glasgow, consisting of upcast and downcast shafts fixed above deck, communicating with the interior of vessel by a system of piping led to the various compartments. The upcast, or “air pump” ventilator, as the patentees term it, consists of a fixed head having an ingenious arrangement of louvre webs, whereby the wind impinging upon it from any direction, creates a current and exhausts the air from the cylinder of which the head is part, the foul air from below immediately ascending to supply the place of the air extracted. A continuous and powerful upward current is thus induced, and the head is so devised as to effectually prevent down-draught or the inlet of water. The elevation and plan of this ventilator is shown by Figs. 12 and 13. In Fig. 13, 1 represents cylindrical chamber communicating with shaft below; 2, deep lip to prevent the possibility of water passing into cylinder and down the shaft; 3, curved plates to deflect and compress the air over outlet openings or slits; 4, creates an induced current and exhausts the air from the cylinder; 5, radial plates to deflect air off centre of slits; 6, curved baffle plate or guard, to concentrate the current, and prevent the wind blowing through the slits opposite. The downcast ventilator, though necessarily more simple, is arranged, by means of similar louvered webs to prevent any water passing below, lodging it on the open deck instead. By means of up and downcast ventilators of this type, it is possible to have the ventilation going on between decks without interruption when there is a storm blowing and seas sweeping the deck, whereas under ordinary conditions, and in similar weather, everything would be battened down and the ventilation _nil_. The