Summary

Chapter 18, “Spying with Invisible Light,” is divided into seven subsections. Muller uses the term “invisible light,” to refer to infrared, radio, radar and x-ray waves. All of these move the same energy as light waves, but are not visible to the human eye, and so equipment is needed to detect them. Muller once got a demonstration of this from U.S. Border Patrol, who use infrared binoculars to detect people moving across the border at night.

“Infrared Radiation,” or heat radiation, is emitted by all living things whose atoms move. It has too low a frequency to be detected by the human eye, but devices that can pick it up can create a picture for people to view either through specialized lenses, like those used in surveillance binoculars, or on a screen.

“Remote Sensing of the Earth,” says that satellites...