Page:Popular Science Monthly Volume 89.djvu/600

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586

��Popular Science Monthhj

��Testing the Lifting Capacity of Balloon Fabric

THE arcomparning photo- graph gives an accurate idea of the great strength of balloon fabric. Six men are shown in a basket suspended from a balloon patch. In the ordinary balloon there are twenty such patches, which means that the huge gas-bag is strong enough, considering only its fabric, to bear the combined weight of one hun- dred and twenty men.

The photograph is interest- ing from another angle. It shows how the ropes are attached to the fabric. The ends of the ropes are first separated into four strands which are frayed out and sewed to the fabric after wliich another layer of fabric is cemented over it. The basket is designed to accom- modate two persons, yet the combined balloon patches have a lifting capacity of more than ten tons.

���The Night Eyes of the Coast Artillery

IN ORDER that the coast of the United States may be guarded by night as well as by day, the officers of the Coast Artillery have dc\cloped a type of search- light larger than any hither- to used in the United States Army. The one illustrated is located at F"ort Terry on Plum Island, where the United States maintained a militan,' camp for Ijoys this summer.

(juardiiig the entrance of the sound there are fifteen such searchlights. L'nder favorable conditions the beam from one of these giant searchers can "pick up" ships at a range of ten thou- sand yards, or almost six miles. Under

��There are twenty patches in each balloon

��ordinary conditions its range is about seven thousand yards. The light itself consists of the barrel, which is a large horizontal cylinder, in the back of which is a great parabolic mirror which meas- ures sixty inches across. The front of the barrel is closed by plate glass. Between the glass and the mirror an arc plays between two horizontal carbons, capable of develop- ing eighty thousand candle- power. The carbons are fed automatically and last for about five hours when the light is in steady use.

Each searchlight, a unit in itself, is mounted on a truck, by means of which the light may be moved to various points. A motor operating the moving mechanism of the light is connected electrically with the controller which may be at any distance from the light.

By means of this arrange- ment an officer in an observa- tion tower may manipulate the light in any direction de- sired by using a series of levers.

���Under Tavorablc conditions searchlight can "pick up" sh

��the beam from this giant ips almost six miles distant

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