Theory:

This lesson has been written by Sir. C.V. Raman. He has emphasized on the importance of the world's most common liquid. Man has been searching for an imaginary elixir of life for ages - but the true medicine is very near to our hands; it is the simple water. He draws example of the Nile valley civilization to show how one side is the most fertile land on the earth while the other is a sea of billowing sand without a speck of green. Nile river is the life-giving waters that has created and sustained the whole country of Egypt.
 
Water adds beauty to the countryside, be it a small stream or the rainfed tanks that are a common sight in South India. These tanks store the silt-laden water full of nutrients and minerals which are precious to the crops. But they are often neglected and not properly maintained. Swiftly flowing water carries fairly large and heavy particles while the finer particles which are more in number are carried to great distances.
 
The flow of water plays a great beneficial role in the geological process of converting rocks into soil. India, an agriculture-based country, depends on seasonal rainfall/snowfall, as it is the only source other than the artesian water. Conservation of rainwater becomes a huge responsibility when soil erosion is not checked. Soil erosion though may not be evident at first; it is painfully apparent at the later stages when deep gullies and ravines are formed, rendering agriculture impossible. It calls for urgent preventive action - terracing of land, construction of bunds, contour cultivation and planting appropriate types of vegetation are some of the measures suggested by the author. These measures serve a double purpose of preventing soil erosion and keeping the water on and in the soil.
 
The author also brings in other benefits of water like using boats for a cheaper transport system and hydro-electric power, which can uplift rural areas of India. Water is both the most common and uncommon liquid. The investigation about the nature and properties of water will always be of the highest scientific interest!
 
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Water - the elixir of life!