The Street Letter Box: A Lid That Is Also an Air-Lock

Downing's improvement is to "the lid or that portion through which mail-matter is introduced into the box", shown on "the upper part of a street letter-box." The cover A is hinged to ears a and normally closes the mailing-slot B. Arms D on the cover carry a safety-plate C, pivoted at d, which hangs vertically in the box when the cover is shut. For it to swing "when the cover A is raised from its vertical position" to "close the entrance into the box proper", an abutment or fulcrum E, a rod across the box, is provided: raising the cover draws the plate over it, and the plate takes an approximately horizontal position "and at the same time to cut off communication with the body of the box through the mailing-slot." A transverse plate F between the arms forms, with the guard plate, "a table or shelf upon which mail-matter will be received". "As soon as the cover is dropped the guard plate, being no longer held upward by its abutment or fulcrum, drops and delivers the mail into the box proper." A rib H under the slot prevents "the insertion of a wire or other hook" past plate F, and a hinged "weather-strip" G resting over a storm-rib g keeps "rain or snow" out of the hinge joint.

Make a box from corrugated card with a slot near the top of its front. Cut a lid hinged above the slot with tape, and two arc-shaped card arms fixed to the lid that pass in through the ends of the slot. Pin a card guard plate to the arms, and push a dowel across the box as the fulcrum. Adjust the dowel's position until the plate swings level as the lid is raised and drops cleanly as it closes. Post folded paper letters and check that, with the lid raised, you cannot reach the letters already inside with a bent wire.

**Philip B. Downing** of Boston filed US 462,093 on 2 April 1891; it is dated 27 October 1891. Its claims cover the hinged cover with arms carrying a pivoted guard-plate that rides on a fulcrum, the transverse plate, and the weather-strip. Note: US 462,096, often given for this invention, is a different patent (a carving machine). **Honest limits.** The box size, letter size, packing and lid weight in the notebook are examples.