Magazine article Geographical


Magazine article Geographical


Article excerpt


Q: Is there a numerical relationship between the rings of a tree's branches and its trunk?

A: In compliance with popular myth, you can gauge a tree's age by counting the rings on its trunk. Of course, it has to be cut down for this to happen. Similarly, a branch will have rings for every year of its development. Higher up along the tree, branches will have fewer rings because they are inevitably younger. By subtracting a branch's age from the total number of rings on the main trunk it is possible to track the growth of a tree, calculating when in its life the branch first sprouted.

J Bond, Cardiff


Q: Why does the application of salt to road surfaces produce a thaw?

A: Salt, or sodium chloride (NaCl), is a commonly found and inexpensive crystalline compound that lowers the melting point of snow and ice. The reaction forms a brine or strong saline solution that further penetrates and melts the ice and prevents the water from freezing again once it has thawed. It is also an endothermic reaction because it produces heat. The solution of salt in water has a lower vapour pressure than the ice so that it changes its state to liquid water. The lowest temperature at which salt melts ice is -21.12 [degrees] C. However, salt works best at temperatures just below freezing, which is fortunate as this is when most snowstorms occur.

Andrew J Webber, Nottingham


Q: When was the dating system AD/BC first used and by whom?

A: The concept of the Christian Era was invented by a man called Dionysius Exiguus (c.500 to 550AD) in about 525, at the request of Pope St John I. It commenced on 1 January, 754AUC (anno urbis conditae -- in the year of the foundation of Rome). Dionysius Exiguus, a Scythian monk or abbot who lived in Italy, declared the years before the Nativity as BC (before Christ) and those after as AD (anno Domini, in the year of the Lord). …

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