Ask Mr Brain...all will be explained

PUBLISHED : Monday, 04 October, 1999, 12:00am
UPDATED : Monday, 04 October, 1999, 12:00am

How does the Richter scale for earthquakes work? The Richter scale expresses the size of an earthquake by the amount of energy released at its focus, or epicentre. It was devised in 1935 by American seismologist Charles Richter (1900-85) and goes on a scale from 0 to more than eight.

While a leap from six to seven does not seem large, on the Richter scale the difference is enormous. The scale is logarithmic and increases by powers of 10. So the energy released by an earthquake measuring seven on the Richter scale is 10 times more than that released by an earthquake measuring six.

The scale is open-ended, so in theory there is no limit to it. However, earthquakes of more than eight are rare, and very destructive. The 1976 earthquake in Tangshan, Hebei, measured 7.8 and left a quarter of a million people dead and the city in ruins. The recent earthquake in Taiwan measured 7.6.

While the Richter scale is the best known, it is not the only way of measuring earthquakes. The earlier Mercalli scale, named after Guiseppe Mercalli (1850-1914), measures earthquakes in terms of how they affected the people in the area. An earthquake of one on the Mercalli scale would rarely even wake people who were asleep, while one of 12 meant total destruction.

Why can people sense light even when their eyelids are closed? CYNTHIA SIU Methodist College Since our eyelids are thin pieces of skin, we can sense bright light even when our eyes are closed.

Recent research suggests that our eyes are not the only part of the body able to sense light. For a long time scientists wondered how blind people's body clocks could work the same as sighted people's, since they could not tell whether it was day or night. And yet blind people get up and go to bed with the hours of daylight and darkness.

Last year, in a rather strange experiment, scientists at Cornell University in the United States reported that they had been able to reset people's body clocks by shining in tense light on the back of their knees. The scientists believe that the secret of the biological clock lies in the cells, not in the eyes.

Earlier experiments at the University of Pennsylvania had uncovered a plant gene, called cryptochrome, which responded to blue light - the kind of light found around dawn or dusk. Other researchers found two genes in human DNA which responded in a similar way. From this, scientists believe certain genes control the body clock by detecting blue light and sending signals to the brain. These genes are found in muscles, skin and brain, as well as in the eye.

This, the researchers say, is why blind people can set their own body clocks and why light shone on the back of the knees affects the body clock, which could help travellers overcome jet lag more quickly.