Clouds are formed when water evaporates from rivers, ponds, oceans, and lakes. The tiny droplets of water cling to particles like (dust, salt, or smoke). The air containing this evaporated water vapour rises and expands at higher altitudes where the air pressure is lower and clouds move with the wind. High cirrus clouds are moved by a jet stream and …

If an astronaut leaves his spacecraft during a journey, he cannot walk about in the ordinary way. There is nothing but empty space. There is not even any gravity to pull him in one particular direction. He can only guide himself by the same means as the spacecraft itself – by rocket propulsion. So when astronauts do leave their spacecraft …

On contact with an allergent, chemical substances are released from mast cells and basophils. The chemical mediators (e.g. histamines) in turn attach themselves on to H-1 receptors to produce allergic effects. Anti-allergen drugs block these chemical mediators. The drugs also produce down regulation of H-1 receptors.

The sun is the driving force in all of the Earth’s processes. It is the sun’s rays that keep our planet warm enough for us to be able to survive, it is the weather’s motor, and provides energy for the most important process of all so far as plants and animals are concerned. The sun provides plants with the energy …

Having a tooth extracted or drilled may not be pleasant but-thanks to anaesthetics-at least it’s not painful. These drugs also prevent pain in surgical operations. We feel pain because electrical signals flash along the nerves in our body from the part that hurts to the brain. Anaesthetics interfere with the nerves so that these pain signals are locked. A general …

This is another term for goose-flesh, because cold or fear causes the skin to look like that of a plucked goose. What happens is that when we are cold or receive a fright or shock, nerves which control the tiny muscles at the roots of the hair are disturbed. As a result, these muscles cause the hair to stand on …

When the sun was born from an immense cloud of gas and dust 4,600 million years ago, it is thought to have been surrounded by a disk of surplus material. Gradually, this disk formed into a number of smaller, cold bodies orbiting the sun. The planets were born. Hence the planets are the left-overs from the birth of the Sun. …

An Italian astronomer Galileo Galilei was the first person to work with telescope. In the beginning of 1609, he disclosed the details about the surface of the sun and the moon, Jupiter’s moon and Saturn’s rings, and discovered many stars too faint to be seen with the naked eye. His observations of the solar system led him to support the …

The early seamen sailed by the sun and stars, rarely venturing out of sight of the land. Then the Chinese discovered the lode-stone or guiding stone, and the fact that it always pointed to the magnetic north. It was first used in Europe in the twelfth century, and the idea of attaching it to a compass card is credited to …

The Cutty Sark was one of the last of the clipper ships specially built for the tea trade between China and Britain. Her unusual name was taken from the witch in Robert Burns’s poem ‘Tam O Shanter’, and her figurehead represented a witch. She carried a great spread of canvas and it was said of her that in her day …