“Here is the chronoscope,” he said.

“The latest development of the instrument. Scansion depends upon a special curved field, through which a sub-etheric radiation is bent into the time-axis, projected forward, and reflected from electronic fields back to the instrument. A stereoscopic image is obtained within the crystal screen, through selective fluorescence to the beat frequencies of the interfering carrier waves projected at right angles from below. But I’ll show you Gyronchi.”

(Chronoscope from 'Legion of Time' by Jack Williamson)

THE OLD MAN snapped a switch, manipulated dials at the end of the crystal block. It lit with a cloudy green. The green cleared, and a low cry escaped Lanning’s lips.

For, microscopically clear within the crystal, he saw a miniature world. A broad, silver river cut a fertile green plain dotted with villages. Beyond the river rose two hills.

One was crowned with a tremendous castellated citadel. Its frowning walls and mighty towers were gleaming red metal. Above them flowed banners of yellow and crimson and black. A massive gate opened in the foot of the hill, as he watched, and an armored troop poured out.