Boyle’s patent self-acting air-pump ventilators are well known, and are found to answer well in their continuous action under all varieties of wind pressure; they are often adopted without any inquiry being made as to the scientific principles on which they are constructed. They consist of 4 sections, each acting independently of the other. The exterior curve baffle-plate prevents the wind blowing through the slits formed in the immediate interior plates, and tends to concentrate the current. These interior plates are curved outwards, so as to take the pressure off the vertical slits, which form a communication with the internal chambers, through which the air impinges on inner deflecting plates, and is further directed by the radial plates. The external air impinging on the radial plates is deflected on to the side plates, and creates an induced current. In its passage it draws the air from the central vertical chambers, expelling it at the opposite opening. The vitiated air immediately rushes up the shaft connecting the ventilator with the apartment to be ventilated, extracting the air and producing a continuous upward current without the possibility of down draught. The partitions separating the chambers prevent the external air being drawn through the slits upon which the wind is not directly acting. The whole arrangement being a fixture, with no mechanical movement, it is never liable to get out of order, and the apparatus can be easily fixed over a wood base or frame covered with zinc or lead to secure a good water-tight connection. Where Boyle’s ventilators are used the air is renewed imperceptibly, the vitiated air being extracted as rapidly as it is generated.