Popular Science Monthly 



115 



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 



