Page:Popular Science Monthly Volume 90.djvu/849

 The Mangrove Shields of the Savages

��The implements were crude but the product was serviceable and artistic

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��A scar left on a mangrove tree from the tearing away of bark for a shield

IN the days when the savages of the New South Wales coast fought with spears and boom- erangs, a stout shield was an im- portant part of the warrior's equipment. White men, with their firearms and their tools of steel, had not yet arrived. The Stone Age had not given place to the Age of Iron.

Nobody knows when the first enterprising native discovered that the gray mangrove tree could be made to yield a shield of un- rivaled toughness by a compara- tively simple operation. This con- sisted of cutting through the bark of the trunk an oval groove, or rabbet, two or three inches deep. Into this groove were inserted a number of wedges made from a special kind of stone. By driving these wedges in with a stone ham- mer, a layer of wood was brought away in a single piece; then a little trim- ming and the attachment of a bit of twisted vine sufficed to convert the piece into a perfect shield.

In the Port Macquarie district almost every gray mangrove tree of suitable size has been made to yield such a shield, and in many cases two or more shields have been taken from one trunk. The conspicuous scars remain to tell the story of a vanished art. Some of these scars are believed to be

����The perfect shield, trimmed, polished and provided with a handle made of twisted vine tendrils

��Driving the stone edges in around the oval piece of bark marked off

more than five hundred years old, while some are relatively modern, and were made with steel axes.

The earliest English shields were "bucklers" of lindenwood and were made in much the -ame manner as these mangrove shields of the savages, except that they were provided with strong iron ribs and bosses.

��Throwing Heat Overboard from Ocean Steamers

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��N all sea-going steamers, the steam is condensed by sea- water pumped through the surface condensers. This circulating water is then discharged overboard. In the process of condensation, the cooling water taken in at tempera- tures varying from 32 degrees to 88 degrees Fahrenheit according to climatic and other conditions, is raised to •temperatures varying from 80 to 120 de- grees and then discharged. This great loss of heat is practically unavoidable. Even on comparatively small steamers, hundreds of tons of heated water are pumped overboard daily. This constitutes one of the greatest heat losses in the operation of steam ma- chinery, although sometimes a portion of the warm water is used for scrubbing decks and for bath water on passenger ships.

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