The Sea Spectroscope

This is certainly an idea whose time has passed but I find it intriguing anyway. There is a navigation tool that would have been extremely useful in the days of sailing ships hundreds of years ago except that it seems no one ever thought of it. The telescope was invented by a Dutch maker of eyeglasses and used with great effect for astronomical observations by Galileo. Ship captains often carried hand-held telescopes to sea.

In 1666, Isaac Newton discovered that white light, which is a mixture of all colors (colours), can be broken down into it's component colours by passing it through a glass prism. This was the beginning of the spectroscope. (Note: to avoid continuous use of parenthesis, I will alternate the two global spellings of the word color or colour).

As I pointed out in the posting "Plants and Light", the daytime sky contains every major color except much green and this is why plants are green. Clouds are white because the droplets of water in them do the opposite of a prism, they merge all colours together into white light. All colors, that is, except green but our eyes cannot tell the difference whether much green is included or not.

The thing that surprises me is that no one thought of combining a telescope with a prism and taking of it to sea. If the scope was focused on a cloud near the horizon, it would quickly tell the captain whether land was near. No significant amount of green light comes from the sky and the water absorbs blue light last so the sea is blue. This means that if the cloud was shown to contain green light, it can only be from land under the cloud. The same technique could be used to tell travellers on land whether they were near a large body of water.