A somewhat similar arrangement to Boyle’s ventilator is patented by Arnold W. Kershaw, of Lancaster, and consists of 3 rims of deflectors or plates with openings in each, so arranged that the openings in one rim are opposite the deflectors in the next inner or outer rim, the effect being that whatever the direction of the wind, it passes through the ventilator without being able to enter the central shaft, and in passing creates a partial vacuum, which induces an upward current in the upcast shaft without the possibility of down draughts. Both Boyle’s and Kershaw’s roof ventilators are suitable for fixing in ventilating towers or turrets. While Kershaw’s is somewhat simpler in construction, Boyle’s is said to possess the additional advantage of preventing the entrance of snow by the curve in which the inner plates are fixed. In the case of chimney flues where there is any obstruction that breaks the wind and produces a swirl, such as would be caused by close proximity to higher buildings or raised gables, a down draught may be prevented by the use of a properly-constructed chimney cowl. Kershaw’s chimney cowl is a modification of his pneumatic ventilator, and consists of deflecting plates so arranged that there is no possibility of a down draught. Boyle’s chimney cowl is better known than Kershaw’s, and is very effective. It consists of deflecting plates so fixed that if a body of air is forced in at the false top, instead of passing down the vent, it is split up by an inner diaphragm, deflected over the real top, and passed over at the side openings, thus checking the blow down and assisting the up draught. Kershaw’s patent inlet and air diffuser consists of a tube connection between the outside and inside of an apartment rising vertically on the inside, the upper extremity having radiating plates, which diffuse the incoming current. Generally speaking, a sufficient amount of fresh air enters under the door to a room or between the window sashes or frames; but in apartments where doors and windows fit tightly, some arrangement for the admission of fresh air becomes indispensable. In this climate, during 7 months of the year, the external air is usually too cold to be admitted directly into the room. The plan of admitting fresh air to a space behind the grates, leading up the air through channels on each side of the fireplace, and ultimately passing it through perforated gratings within the wall or through perforations in the skirting board on each side of the fireplace cannot be commended, as the passages are apt to get choked up with dust, and the temperature of the air cannot be well regulated in its passage into the room. The true object of a fire and chimney flue should not be to supply fresh air, but to extract it after it has done its work. [Illustration: 29. Boyle’s Air-cooler.]