AIR-PIPES. An invention for clearing the holds of ships and other close places of their foul air. The contrivance is simply this: A long tube, open at both ends, is placed with one end opening into an apartment to be ventilated, and the other out of it. The air in the outer end of the tube is rarefied by heat, and the dense air from the hold comes in to supply the partial vacuum, the escape of the foul air in the hold being supplied by, fresh air introduced through an opening above; and this process is carried on until the air becomes everywhere equally elastic.