# Page:Popular Science Monthly Volume 91.djvu/760

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��Popular Science Monthly

��ground, no matter how obliquely; the tester knows that the eccentricity of the fixture, due to its unbalanced distribution of weight, is greater than that of the shell, due to its uneven distribution of metal about its axis. Should it, however, point upward, the reverse is true.

The weight and offset of the eccentricity weight are proportioned to agree with the maximum allowable variation from perfect balance of the shell, so that, if the weighted end of the fix- ture points upward the shell fails to pass the test, while if the weighted end points toward the ground on coming to rest, the sjiell passes mus- rer.

How far off balance may the shell be? Ina 120-milli- meter French shell — a pro- jectile slightly less than 4^ inches in di- ameter and weighing, un- loaded, close to 40 pounds — about the dis- tance between two pin scratches placed as close together as possible without touching.

The balance of the shell lengthwise is more easily found. All that is necessary is to balance the shell on knife edges, much as one would balance a pencil on one's finger. The point of balance must be at a definite distance from the base of the shell. A variation of more than one per cent, in the length is sufficient to disqualify the shell.

���French Official Photo

What the French have in store for German airmen — the famous French "75" mounted on a motor-truck chassis

��A French "75" Anti-Airplane Gun with a Camouflage Dressing

THE French have found still another use for the versatile "75." They have mounted it on a motor-truck chassis, heavily armored, and have sent it close to the front to pepper German airplanes. The accompanying illustration shows the new combination of motor-truck and big gun and the crew of three that operate each unit. The truck is painted and covered with boughs to hide it from the eagle eye of the enemy air scout.

Look close- ly at the pho- tograph and you will see that the truck is pro- vided with stabilizers in the form of iron legs or jacks which actual- ly anchor the truck body to the ground. These stabilizers are located one behind each rear wheel, one on each side of the truck in front of the rear wheels, and one behind each front wheel.

When the truck is moving, the stabilizers are carried in an inoperative position, but as soon as the truck stops and the command to attack an enemy squadron of airplanes is given, the six stabilizers are forced into the ground, giving the big gun a firm foundation to fire from.

��Train Your Skin So That It Will Not Be Sensitive to Cold

ris pretty generally believed that ex- posure to cold and wet weather will bring on the disorder known as a "cold." But sensitiveness to cold is usually due to the fact that the nerve centers controlling the circulation of blood through the skin are over-delicate, and exhibit a sort of hair- trigger reaction to exposure. By accustom- ing the body gradually to cool and later to cold baths, resistance to cold is set up.

��Sixty Miles an Hour Is the Climbing Speed of Flying-Machines

A MODERN airplane weighing as much as a small touring car without any passengers can climb at the rate of sixty miles an hour. The aviator would say that his machine's rate of ascension is 1,300 feet a minute. Such an airplane would have an engine of a brake horse- power of 180. The airplane climbing at sixty miles an hour ascends a gradient of 1 in 2> X A to 1 in 4.

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