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Features

Airplane Propeller Manufacture

Problems Which Have Been or Need to be Studied

By A.L. Heim

How a Season Differs from Year to Year

The Rational Causes of Variations in Our Summers and Winters

By Frederic Stupart

Notes on Drop Valves for Steam Engines

Results of Experience With Slow-Speed Land Engines, Perhaps Useful Also in Designing Other Types

By H. W. Morley

Ants of High and of Low Ability

A Study in the Psycho-biology of Various Ants

By Robert Stumper

Printing Silks

Old Hand-Block Printing Contrasted With Present Expensive Power Machines

Recent Progress in Aerial Photography—II

Remarkable Improvements During War and Applications to Peace-Time Needs

By L.-P. Clerc

Light and Organisms

Orienting Effects of Monochromatic Light on Fucus Spores and Rhyzoids

By Annie May Hurd

Gathering Chicle Gum for American Gum Chewers

Collecting, Preparing and Shipping Chicle Gum for the United States

Copying Fingerprints—I

New Methods for “Lifting” or Transferring Fingerprints on Objects by Prepared Paper or Foils

By Robert de R*amp*eacute;sillac-Ros*amp*eacute;

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    September 13, 1919

    Think Outside the Gift Box