human
We knew they were on the coast, said the admiral, a little later, when Metcalf had made his report on the quarter-deck of the _Delaware_.
gpt
But about this light? Are you sure of all this? Why, if it's so, the President will rank you over us all. Mr. Smith came in with the prisoners, but he said nothing of an invisible light--only of a strong searchlight with which you set fire to the signal-yard.
human
I did not tell him all, admiral, answered Metcalf, a little hurt at the persistence of the feeling.
gpt
But I'm satisfied now. That fleet is coming on with incompetents on the bridge.
human
Well, we'll soon know. I've only one ship, but it's my business to get out and defend the United States against invaders, and as soon as I can steam against this gale and sea I'll go. And I'll want you, too. I'm short-handed.
gpt
Thank you, sir. I shall be glad to be with you. But wouldn't you like to examine the light?
human
Most certainly,
gpt
It is very simple, explained Metcalf, showing a rough diagram he had sketched.
human
You see he has used my system of reflectors about as I designed it. The focus of one curve coincides with the focus of the next, and the result is a thin beam containing nearly all the radiations of the arc.
gpt
Very simple, remarked the admiral, dryly.
human
Very simple indeed. But, admitting this strong beam of light that, as you say, could set fire to that sealer, and be invisible in sunshine, how about the beam that is invisible by night? That is what I am wondering about.
gpt
Here, sir, removing the thick disk from around the light.
human
This contains the prisms, which refract the beam entirely around the lamp; and disperse it into the seven colors of the spectrum. All the visible light is cut out, leaving only the ultraviolet rays, and these travel as fast and as far, and return by reflection, as though accompanied by the visible rays.
gpt
But how can you see it? asked an officer.
human
How is the ship it is directed at made visible?
gpt
By fluorescence, answered Metcalf.
human
The observer is the periscope itself. Any of the various fluorescing substances placed in the focus of the object-glass, or at the optical image in front of the eyepiece, will show the picture in the color peculiar to the fluorescing material. The color does not matter.
gpt
More simple still, laughed the admiral.
human
But how about the colored lights they saw?
gpt
Simply the discarded light of the spectrum. By removing this cover on the disk, the different colored rays shoot up. That was to attract attention. I used only white light through the periscope.
human
And it was this invisible light that blinded so many men, which in your hands blinded the crews of the Japanese?
gpt
Yes, sir. The ultraviolet rays are beneficial as a germicide, but are deadly if too strong.
human
Lieutenant Metcalf, said the admiral, seriously,
gpt
Why, admiral, responded Metcalf,
human
Then, unless the Japs are near-sighted, I expect an easy time when I go out.