Page:Popular Science Monthly Volume 88.djvu/54

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T is an old custom in Bohemian bakeries to wipe the boots of visitors as they enter. There is a good deal of wiping these days; for the government and city officials inspect the bakeries at very frequent intervals in order to see that the regulations regarding the amount of flour used in bread are carried out.

The picture shows Dr. K. Gross, the burgomaster of Prague and representatives of the city council, entering one of the bakeries of the city. The burgomaster is the man whose boots are being wiped.

NE of the most interesting facts brought out in Germany's submarine campaign against British commerce was the accuracy with which the British guns were trained upon occasional indiscreet periscopes.

The periscope tube is small, and an especially difficult target at long range, vet on a few occasions—occasions which were so recurrent that the accuracy could not be attributed to accident — British guns have demolished periscopes, thereby rendering the submersible helpless—an easy prey when she came to the surface.

Nor can this remarkable accuracy be attributed entirely to the correctness of the gun design. The fact of the matter is that the British method of range-finding, aside from being one of the most interesting, is one of the most accurate in the world.

Whether the enemy appears in the form of a glinting periscope on the water, a black dot, or a ship on the horizon, the method of range-finding is fundamentally the same. A range-finder works on the same principle as that by which we can estimate a distance with our eyes. Lines drawn from our eyes to the object form sides of an angle. The size of this angle determines the distance. Unconsciously and automatically we reckon distances by the complicated process known as triangulation.

What we estimate roughly with our eyes, range finders determine accurately