The Adjustable Window Screen: Two Frames That Slide to Fit

"I construct the window-screen in two parts, each part consisting of two frames, A and B, each being covered with wire gauze, or any suitable screen-cloth." Metal strips on frame A form a guide for frame B: "The object of this construction is to admit of one frame sliding over the other, to adapt the width of the screen to the widths of different windows." An adjustable cross-piece is "intended to be always kept in said frame, directly over the end piece H of the frame B, so that there may be no space between the end piece H of the frame B through which insects can pass." In his earlier patent the cross-piece ran in grooves on tenons, and it stuck or fell out. Now "The spring causes the cross-piece to adapt itself to the variations in the sizes of the frames, and move readily to the position desired."

Lay a ruler on the screen mesh and count the wires in 25 mm under the loupe; that is the mesh count per inch. Measure the wire with the caliper. Put both into the notebook to get the hole size and the open fraction. On a breezy day, hold the anemometer in the middle of an open window and read the air speed, then set the screen in the opening and read it again at the same spot. Compare the drop with the open fraction.

**Daniel N. Hurlbut** of Chicago received US 99,197, dated 25 January 1870. It improves on his own screen patented on 1 June 1869; his claims are the spring behind the cross-piece and the lipped guide strips. **Honest limits.** Open area is only a first guide to airflow; the wires also add drag. The insect sizes are examples, and insects squeeze through smaller gaps than their resting width. Your anemometer readings are the measurement.