Kennedy had jumped to the window. I followed to restrain him,
fearing that he had some mad scheme for climbing out. Instead,
quickly he placed a peculiar arrangement, from the little package
he had brought, holding it to his eye as if sighting it, his right
hand grasping a handle as one holds a stereoscope. A moment later,
as I examined it more closely, I saw that instead of looking at
anything he had before him a small parabolic mirror turned away
from him.

His finger pressed alternately on a button on the handle and I
could see that there flashed in the little mirror a minute
incandescent lamp which seemed to have a special filament
arrangement.

The glaring sun was streaming in at the window and I wondered what
could possibly be accomplished by the little light in competition
with the sun itself.

"Signaling by electric light in the daytime may sound to you
ridiculous," explained Craig, still industriously flashing the
light, "but this arrangement with Professor Donath's signal mirror
makes it possible, all right.

"I hadn't expected this, but I thought I might want to communicate
with Burke quickly. You see, I sight the lamp and then press the
button which causes the light in the mirror to flash. It seems a
paradox that a light like this can be seen from a distance of even
five miles and yet be invisible to one for whom it was not
intended, but it is so. I use the ordinary Morse code--two seconds