The World's Most Powerful Searchlight 



It sends forth a beam as brilliant as fiercest sunlight 



IT is ten feet high, its mirror has a diame- 

 ter of five feet, and it weighs three tons. 

 Its beam is as brilhant as the sun at 

 eight o'clock in the morning or four in the 

 afternoon. New York latitude, and you can 

 read a newspaper by its light thirty miles 

 away. The heat of its focused beam is so 

 intense that it will set paper afire at a dis- 

 tance of two hundred and fifty feet. It has 

 a candlepower of more than one and 

 a quarter billion. 



These are a few astonishing 

 facts about the Sperry search- 

 light, the invention of Elmer 

 A. Sperry, of Brooklyn, 

 N. Y., who is already known 

 as the inventor of the air- 

 plane stabilizer and ship 

 gyroscope bearing his 

 name and the first elec- 

 tric arc light. When the 

 last big air raid over 

 London was made by Zep- 

 pelins, the Sperry search- 

 lights bathed the big dirigi- 

 bles in beams of light they 

 could not escape. According 

 to some London accounts the 

 Sperry searchlight is the 

 Zeppelin's Nemesis. 



One of the most powerful 

 beacons along the coast is the 

 Sandy Hook Lighthouse. But the Sperry 

 searchlight is twenty-two times more bril- 

 liant than that light. Were the Sperry 

 lamp substituted for the lighthouse beacon, 

 a ship passing out to sea could be bathed in 

 light until it disappeared below the horizon. 

 By swinging the light back and forth across 

 the sky it has been made visible one hun- 

 dred and fifty miles away. For Navy use 

 the Sperry lamp illuminates a target ten 

 times more brilliantly than any other pro- 

 jector devised. 



Equipped with a carriage that permits 

 the lamp to be turned in a circle and in any 

 direction up to ninety degrees, the giant 

 searchlight is of the greatest value in 

 detecting aircraft. The operator can not 

 control it near at hand; the great heat 

 prevents that. He must stand fifty feet 

 away. At that distance he is able to 

 focus accurately upon any moving object. 

 Because the rays projected by the lamp are 



Elmer A. Sperry, inventor 

 of the greatest searchlight 



nearly parallel, there is no diffusion of light 

 over a wide area. The beam is concentrated. 

 When the searchlight is being operated, 

 the temperature of the arc is nine thousand 

 degrees Fahrenheit- — seven thousand de- 

 grees higher than the melting point of the 

 metal holders of the carbons. Conse- 

 quently, in order to prevent these parts 

 from melting, a current of air is forced, by 

 means of a motor-driven blower, 

 through the carbon supports and 

 discharged through the heat- 

 radiating disks that surround 

 the holders. In the Beck 

 lamp the holders are 

 sprayed with alcohol to 

 prevent thern from melt- 

 ing. 



The several factors 

 which combine to make 

 the Sperry lamp so power- 

 ful are the small elec- 

 trodes, the special carbons 

 used, the manner in which 

 they burn and the parabolic 

 mirror. A colored glass peep- 

 sight enables the operator to 

 watch the arc without being 

 blinded by the glare, or the 

 arc is reproduced by lenses 

 upon a ground glass outside 

 the lamp. An iris diaphragm 

 similar to that used on cameras, regulates 

 the light. 



Stand in the beam of the Sperry lamp at 

 any distance closer than three hundred feet 

 and your skin will be burned. At that 

 distance the skin peels. The great heat of 

 the arc is due to the fact that it produces a 

 crater which more nearly approximates the 

 mathematical point of light than does that 

 in other searchlights. The candlepower is 

 more than three hundred and twenty 

 thousand per square inch. 



Designed for naval and military pur- 

 poses, the Sperry lamp, in addition to 

 locating enemy forces on land and in the 

 air, is useful also in throwing a screen of 

 powerful light in front of the enemy. It is 

 impossible to see through its concentrated 

 beam. Allied field forces have mounted 

 the lamp on armored cars and have found 

 it available for signaling at any distance 

 up to one hundred miles. 



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