Note 70 — Chapter VI · THE ATMOSPHERIC SYSTEM. A.D. 1840—1848. ÆTATIS 35—43.

This valve consisted of a number of long delicate blades of spring steel, arranged parallel to each other, as in a musical box, but with wider intervals. These plates rested on a series of truly faced bars, which crossed the end of the air-passage. The slightest pressure outwards lifted the springs; and as the area of opening was large, a very free passage was given to the air. On the current ceasing, the blades instantly, yet without shock, replaced themselves in contact with the bars, clipping them tightly under a very small reverse pressure, and effectually closing the passage. Their merit consisted in their being almost without weight, and thus promptly re-closing the aperture by a delicate elastic reaction.