An experimental Christmas
I HOPE you are enjoying your Christmas festivities. Christmas Day is of course a celebration of the birth of Jesus Christ. It is a good day to have a birthday.
You may not know it, but Sir Isaac Newton, the discoverer of gravity, was born on Christmas Day in the year 1642. Along with his theory of universal gravity this remarkable man gave us so many great discoveries.
One could almost say that he was the powerhouse for the sudden explosion of science in the 17th century.
Newton spent his entire life pushing back the frontiers of knowledge. He would theorise, experiment, then find that he was limited by the technology that was available. For example, in his mathematical work he had to invent differential calculus in order to progress further.
Similarly, in astronomy, he found that the refractor telescopes in use produced a type of distortion called chromatic aberration. This means that light is split by the prism effect of the lenses, so that coloured distortions hamper viewing. Accordingly, he invented the reflecting telescope, which works by using a mirror to collect the light rather than lenses. It enabled much larger telescopes to be built so that astronomers could see further into space.
But this is Christmas, and you don't want to hear a lecture about Isaac Newton. So as a little novelty, why not try this experiment this Christmas. It is a phenomenon that was discovered by Professor John Tyndall in the 19th century. He would not have understood it without Newton's work on optics and colours.
Get a wine glass and put four or five drops of milk in the bottom, then fill it up with water. You need to dilute it so much that it just produces a smoky-blue coloured water. Now get a torch with a very fine beam (shine a beam through a small hole in cardboard, perhaps) and darken the room. Then shine the torch through the glass.
You will see a definite beam passing through the liquid. Look closely and it will seem to be slightly blue. Now aim at the beam through the glass at a white wall. This will have a definite red tinge. If you look through the glass at the light source, it will shine red.
You have produced a Tyndall Effect. This is all about light scattering. The dispersed globules of fat in this very weak emulsion are
scattering the shorter blue wavelengths of light more strongly than they do the red wavelengths. The beam of light that you see going through the emulsion is caused by the scattered blue rays. If you were to just shine the beam through water you would not see a beam, because the light is not scattered and the emergent light would be white.
The red light spot on the wall is due to the unscattered red rays that hit the wall.
Happy Christmas and watch out for the Blue Moon on New Year's Eve!
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Weather for Wakefield
Wednesday 08 February 2012
Today
Sunny spells
Temperature: -4 C to 2 C
Wind Speed: 9 mph
Wind direction: South
Tomorrow
Light rain
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