Page:Popular Science Monthly Volume 91.djvu/131

 Popular Science Monthly

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��An Electric Eye Watches the Smoke Screen During a Battle

THE manner in which the den- sity of the smoke screens is now reg- ulated during a bat- tle is interesting. By partially shut- ting off the draft to her boilers, a battle- ship is made to emit clouds of smoke which screen her from the enemy. But how can the stokers, who are far below deck, see the stacks so that they can regulate the smoke clouds to the proper density? Answer — By an electric "eye." The eye is placed near the top of the smokestack and it records the exact density on electric meters convenient- ly located in the boiler room.

This remarkably clever eye is simply a wire coil of selenium which is carried in a housing on the inside of the smokestack walls. An electric light, in another housing directly opposite, plays its beam of light squarely upon the wire. Now selenium, as is well known has the peculiar property of changing its resistance to an electric current when the light falling upon it changes. The weaker the light, the greater the resistance, and vice versa.

Evidently then, the denser the smoke emitted through the stack, the weaker the light that gets through the smoke from the electric lamp and falls upon the selenium. By connecting the selenium with an electric meter

���Lamp control

��The selenium cell is sensitive to light. Hence when the smoke shuts off the light it can " see " what happens in the stack

��and the ship's lighting mains, the electric current going through the meter will be lowered by the increased resistance. The meter is very sensi-' tive and shows the slightest change in smoke density. Moreover, it is cali- brated to indicate exactly what the actual smoke densi- ty is, so that the stokers can regulate the cut-off of the draft to a nicety. Glass plates are placed in front of the lamp and of the selenium coil to pro- tect them from soot. The plates are kept clean by streams of compressed air di- rected across them. This device was in- stalled on the U.S.S. Conyngham and was called to the attention of the So- ciety of N.aval Ar- chitects and Marine Engineers by Rear Admiral R. T. Hall, U. S. N.

��An Ice Helmet to Relieve the Fever Patient Without Disturbing Him

THE principal defects of the ice caps so frequently used on the heads of fever patients are that they do not fit the head, they can not be refilled with cracked ice without re- moving them from the patient and the water can not be drained off.

A New York city in- ventor, M. Finkelstein, seems to have overcome all these shortcomings in devising the ice cap illus- trated. A screw-top opening permits the nurse to replenish the cap with cracked ice without disturbing the patient, and a drain pipe is provided.

���The ice helmet which can be drained and refilled without disturbing the patient. It fits the head securely

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