Page:Popular Science Monthly Volume 91.djvu/238

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222 Popular Science Monthly

A Ten-Thousand -Dollar Map of



���The map is a segment of a 90-foot globe, with heights and depressions clearly represented. Every battlefield is shown

��Warring Europe

the lobby of one of Chicago's large office buildings is a huge relief map of the European countries where the war rages, exhibited to the public and lectured upon by a former war correspon- dent. The main map is io x 20 feet, but owing to its convex construction it contains an area of 300 square feet. It is a seg- ment of a 90- foot globe. It was made by William Rob- ertson, with the assistance of ten men.

It took them nine months to make it. Including labor and materials, the cost of the map is estimated to be $10,000.

A special feature of the map is a system of small incandescent lamps which are flashed in connection with a large signboard made up of two hundred small transparent illuminated signs, each bearing the name of an important point on the map. When the lecturer mentions an important point in the war territory a light flashes at that point on the map and simultaneously the name is flashed on the large sign which is located at the left side of the map. This makes it possible for the spectator to follow the lecturer more closely and in- telligently.

The method used in constructing the map is interesting. A work- ing model was first made. From this the frame was laid out, the map scaled and the countries outlined. The vertical parts were next

��scaled and little pegs driven down for measuring the mountains. A clay map was then made on this frame and a cast taken, from which the plaster of Paris map (the one on display) was made. The next task was to shave the map and gradu- ate it, after which the various parts were indi- cated and colored. At the same time the wiring system for the incandes- cent lights was installed. The scale of the map is one inch to every 7.8 miles . It shows the topographi- cal detail of every battle- field.

���A simple bell-action attracts the arma- ture and re-tightens the helical driving- spring whenever the watch runs down

��An Electric Self- Winding Clock for the Automobile

WEAK-CURRENT electricity is in- terestingly applied in the self-wind- ing mechanism of a clock which has been specially designed for the dashboard of the automobile. A simple electromagnet is made to drive the clock, and but three or four batteries are required.

In construction, this clock dif- fers little from any other. The gears, however, are mounted to withstand the jolts of traveling. And instead of the or- dinary hair-spring a straight helical spring furnishes the motive power. The armature of the elec- tromagnet works much like that of a bell ; it tightens up the driving-spring every time it is attracted to the magnet. The spring loosens up while running the clock, the armature swinging slowly back.

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