"I'll say I wouldn't!" she exclaimed, feelingly.
"Well, anyway, by the use of suitable fields of force it can be used as a carrier wave. Most of this stuff of the fields of force—how to carry the modulation up and down through all the frequency changes necessary—was figured out by the Martians ages ago. Used as a pure carrier wave, with a sender and a receiver at each end, it isn't so bad—that's why our communicator and radio systems work as well as they do. They are pretty good, really, but the ultra-light vision system is something else again. Sending the heterodyned wave through steel is easy, but breaking it up, so as to view an object and return the impulses, was an awful job and one that isn't half done yet. We see things, after a fashion and at a distance of a few kilometers, by se
