Ask Uncle Pai — Why do little children wear big glasses?

Dowsers make use of a forked piece of willow wood to detect hidden substances such as water and metal, below the surface of the earth. The dowser grabs the rod by its two prongs and appears to receive transmissions from the hidden water (or metal) that causes involuntary muscular contractions, which in turn make the rod quiver.

In India during the 1950s, a man popularly known as Paniwalla Maharaj helped in locating underground sources of water in Gujarat. Russians too have used the services of the dowsers to detect sources of water and underground mineral deposits.

QWhy do some children have to use spectacles from a very young age?

— R Anusha, Dombivli

Eyesight has a lot to do with heredity. Reading in dim light and watching TV for long, from a close distance particularly in total darkness affect the eyes adversely. Eyesight is also affected due to the deficiency of Vitamin A.

QWhy is the Black Box searched after an air-crash?

— A Maharaja, Pune

The Black Box or the Flight Data Recorder is, in some respects, like a taperecorder. Its purpose is to help investigators pinpoint the causes of air accidents.

The Black Box receives and records signals from a variety of sensors that monitor at least 17 different performance statistics of an aircraft like its speed, the rate of climbing, engine thrust, altitude, etc. If there is an accident, the Black Box along with the cockpit voice recorder is a witness to the disaster. It is therefore of utmost importance.

QWhy do we urinate more often in the rainy season?

— NandKishor Sawant

We tend to urinate more often not only in monsoon, but also in winter. When the weather is cold, we do not perspire. It is only when the weather is warm that we perspire a lot. When the perspiration dries up (turns into vapour) it takes away some body heat in the form of latent heat of vapourisation. In the process the body is kept cool and the body also loses some water. This leaves less water in the body to be thrown out in the form of urine.

In winter and monsoon, we don’t sweat much and very little water is thrown out of the body in form of perspiration, therefore we urinate a lot.

QWho invented the calendar, the days and weeks? How? When?

— Haresh Kithani,Ulhasnagar

From time immemorial, people have had their own methods of marking time. The calendar was not invented in a particular country. In ancient India, ancient Babylon and in ancient Greece the basic unit of computation was the day, from sunrise to sunrise. Now, a day is counted from midnight to midnight. In Europe a day was measured from noon to noon.

A day was divided in different ways. In ancient India, a day was divided into eight prahars. Each prahar was equivalent to three hours. Sumerians and ancient Jews divided the day into six watches. The Babylonians had divided the day into 12 parts (equivalent to two hours each).

The next task was to gather days into groups. Some had groups of four days and some of five. Babylonians decided on the number seven, probably because of the seven celestial objects known at that time: Sun, Moon, Mars, Jupiter, Venus, Saturn and Mercury. They had a seven-day week.

A year is the period taken by the earth to complete a revolution around the sun. The lunar month is the period in which the moon completes a cycle of its phases, lasting approximately 29.5 days. The difficulty arises from the fact that lunar (pertaining to the moon) month is not a simple fraction of the solar year.

The era, was different in different country. The Christian era is now universally followed. In India, both the Vikrama era (beginning with 57 BC) and Shalivahana era (beginning with 78 AD) are used.