Miracles Ahead! 



on the tube, and the current flow; a switch is released, and a 

 spring opens the door. 



Phototubes are helping to speed the war effort in many 

 places. In plants where trucks come in and out of doors sev- 

 eral times a day, the phototube opens the door. How long 

 does it take a truck driver to stop his truck at a door, climb 

 down, open the door, climb back up in the truck, start his 

 truck, roll through the open door, stop his truck again, climb 

 down, close the door, climb up in his truck again, and roll 

 on his way? Half a minute? Multiply that half minute by a 

 hundred starts and stops for a thousand trucks, and the loss 

 in man-minutes becomes a loss in man-hours. A doorman on 

 the job could save the truckman's time. But today we cannot 

 spare a man to "stand and wait." The phototube saves that 

 time for us. As the truck approaches, the phototube opens 

 the door, the truck rolls through without stopping, and the 

 phototube closes the door behind it. It would be possible to 

 use that same doorman as a guard, opening the door for trucks 

 of a certain fleet and refusing admission to all others. All that 

 would be necessary in equipping the phototube for this task 

 would be a color filter to protect it from all light rays but 

 those of a certain shade. Then, if the light source reaching 

 the tube were reflected from the passing trucks, rather than 

 interrupted by the passing trucks, only light reflected from 

 trucks of a predetermined color would pass through the color 

 filter and cause the current to flow in the phototube. In this 

 case the flow of current rather than the stopping of current 

 would activate the relays which operated the doors. 



The ability of the phototube to distinguish shades of color 

 has been brought to a high stage of perfection in the spectro- 

 photometer, a device which uses the phototube. While the 

 human eye can sometimes distinguish ten thousand different 

 shades and colors, the spectrophotometer can distinguish two 

 million different shades! 



