Dax shook it violently, and the entire tube glowed brilliant green, lighting the room.

A small tube in the heart of the machine glowed cherry red and the pistons began to move, first slowly, then more rapidly.

I advanced upon the Teacher, and trained the projector upon him, and the tubes glowed properly, and the meters were correctly set upon the base of the weapon.

The great tube glowed.

The tube glowed as it should-but at the same time the lock hummed as the circuits in the base of the lighter sorted through its combinations.

The tubes in the radio glowed.

The tubes still glowed, and a low humming still came from the apparatus.

The tube on the snake's head glowed a deep violet and something like the blades of incandescent knives stabbed into his chest and began to cut slowly across it.

Finally the thing was done, the crude, but efficient graduated circles were set, and the tubes glowed redly as their massed output drove into a tight beam of ultra-vibration.

Under normal operating conditions the tube glows blue and mercury droplets are visible.