What's the name of the tallest mountain in the world?Mauna Kea, the highest point on the island of Hawaii.

The inactive volcano is a modest 13,799 feet above sea level, but when measured from the seabed to its summit, it is 33,465 feet high--about three-quarters of a mile taller than Mount Everest.

As far as mountains are concerned, the current convention is that "highest" means measured from sea level to summit; "tallest" means measured from the bottom of the mountain to the top.

So, while Mount Everest, at 29,029 feet is the highest mountain in the world, it is not the tallest.

Measuring mountains is trickier than it looks. It's easy enough to see where the top is, but where exactly is the bottom of a mountain?

For example, some argue that Mount Kilimanjaro in Tanzania--at 19,340 feet--is taller than Everest because it rises straight out of the African plain, whereas Everest is merely one of many peaks topping the enormous base of the Himalayas, shared by the world's next thirteen highest mountains.

Others claim that the most logical measure ought to be the distance of a mountain's peak from the center of the Earth.

Because the Earth is a flattened rather than a perfect sphere, the equator is about thirteen miles further from the center of the Earth than the poles.

This is good news for the reputation of those mountains that are very close to the equator--like Mount Chimborazo in the Andes--but it also means accepting that even the beaches in Ecuador are higher than the Himalayas.

Though massive, the Himalayas are surprisingly young. When they were formed, the dinosaurs had been dead for twenty-five million years.

In Nepal, Everest is known as Chomolungma (Mother of the Universe). In Tibet, it is called Sagamartha (Forehead of the Sky). Like any healthy youngster, it is still growing, at the not very exciting rate of less than a quarter of an inch a year.

How do moths feel about flames?

They're not attracted to them. They are disoriented by them.

Apart from the odd forest fire, artificial light sources have been in existence for an extremely short time in comparison with the age of the relationship between moths and the sun and moon. Many insects use these light sources to navigate by day and night.

Because the moon and sun are a long way away, insects have evolved to expect the light from them to strike their eyes in the same place at different times of day or night, enabling them to calculate how to fly in a straight line.

When people come along with their portable miniature suns and moons and a moth flies past, the light confuses it. It assumes it must somehow be moving in a curved path, because its position in relation to the stationary sun or moon, has unexpectedly changed.

The moth then adjusts its course until it sees the light as stationary again. With a light source so close, the only way this is possible is to fly around and around it in circles.

Moths do not eat clothes. (It's their caterpillars that do it.)

Where is the driest place on earth?

Antarctica. Parts of the continent have seen no rain for two million years.

A desert is technically defined as a place that receives less than ten inches of rain a year.

The Sahara gets just one inch of rain a year.

Antarctica's average annual rainfall is about the same, but 2 percent of it, known as the Dry Valleys, is free of ice and snow and it never rains there at all.

The next-driest place in the world is the Atacama Desert in Chile. In some areas, no rain has fallen for four hundred years and its average annual rainfall is a tiny 0.004 inch. Taken as a...

JOHN LLOYD is the producer of the hit British comedy shows Not the Nine O'Clock News, Blackadder, and Spitting Image.

JOHN MITCHINSON writes for the British television show QI, and drinks in the same pub as John Lloyd.

From the Hardcover...