Eye that Sees in the Dark

An Eye that Sees in the Dark!

From The Modern Boy magazine, 14 July 1934. Contributed by Keith Hoyt; digitized by Doug Frizzle, May 2013.

SAILORS don't care! Everybody knows that. But there's just one thing that they do care about, and that's fog—they hate it! Fog's bad enough on land, but it's a thousand times worse at sea, particularly in the busy sea-traffic lanes.

Anything which will help the sailor to see through fog is a boon and a blessing indeed. Here's a simple apparatus that is able to feel through it, and send a loud and unmistakable warning when anything is crossing the course on which the ship is slowly moving ahead.

Not only that. It will tell him the direction of every ship all round—even though they may be miles off. And not only ships but rocks, icebergs—any sort of obstruction will send its own signal to this all-seeing "eye."

Actually it consists of a casing something like a searchlight, with a specially shaped mirror at the back. Rays of light, or in this case heat, striking this mirror are reflected forward again, but at the same time they are focused down to a point, always the same. At this point we have the "eye," a little cell called a "photo-electric eye" As soon as the rays strike this cell it wakes up—no it doesn't, for it never sleeps—but it does take extra notice, and sends a signal to the officer on the ship's bridge.

NOW we'll have to step back a bit. You know that the rays of light which come to us from the sun are also rays of heat as well. The rays of light which make all things visible to our eyes also carry rays of heat, though they may be very faint, so faint that you can't notice them. Our friend the photo-electric cell can, though, and he does, instantly.

So long as his mirror looks forward to empty sea and sky there's no change in the heat rays; but if a ship crosses the field of view there is a change. You can imagine easily that the ship is at a different temperature, and it is actually sending out rays of heat, and the electric eye tells us so at once. The funny thing about rays of heat is that they aren't held up by fog as some rays of light are, and that's how this outfit came to be invented. Rays of heat are just a matter of degree; they may be hotter or colder than the average, so our eye gives its signal one way or another.

Inside the body of the apparatus is a pendulum to keep the thing steady in a rough sea, and the whole thing can be moved round and round so as to sweep the horizon.

What sort of a signal does it send? First, it may ring a bell to call attention to any change, and then there will be a pointer on a dial to show hotter or colder. Another dial will give the exact direction from which the signal has come, and probably a third dial may estimate the distance.

How far can this eye see? That depends on how high up it is, but it has worked at fifteen miles!