In the valley of the river Indus, in the west of India (now in Pakistan), remains of unknown civilization were discovered by Sir John Marshall - the Director General of Archaeology in India in 1924. The traces of four cities were found. 'Mohen jo-Daro' and Hadappa were the most important among them.

Natasha asked - "What makes a wind, ma’am?” Ma'am replied - "A wind is simply the motion of air over the earth. What causes the air to move? It's a change in the temperature, which causes all kinds of winds. Whenever air is heated, it expands. This makes it lighter which then rises.

Aeroplanes are machines that fly in the air. Baloons fly because they are lighter than air. Airplanes need engines to lift them up into the air and keep them going. The early planes had no engines. They were like kites of gliders.

Ravinder asked - "Ma'am, water makes up a large proportion of all living things. And it is a tasteless, odourless, colourless thing, what is it?” Ma'am replied - "It is a tasteless, colourless, odourless compound which is present everywhere in the soil and exists in the air.

You find out about what is going on outside your body through your senses. Your eyes work like cameras. Light from outside goes through a hole called the pupil. Through a lense and forms and image on the inner surface of the eye.