Reorganisation · Level 3

Near Sirius, the very bright Dog-Star, is a much smaller star known as The Pup. Being so close to the brilliant Sirius we see it as a faint light, and even then only with the aid of a powerful telescope.

Although smaller, the material at its centre is so dense that one matchbox full would weigh 50 tonnes. It is 27 000 times denser than our sun. The surface temperature is 2 000 degrees hotter than the sun, yet it radiates only a tiny amount of light compared to it.

This type of abnormally small star is known as a White Dwarf, a star that has run out of hydrogen and has no means of reheating. Astronomers believe that these exceptionally dense stars are in their final stages, nearing extinction.

The use of zero has been vital to the development of modern mathematics. The Mayan people of Central America used a symbol for zero in the 1st century AD. Five centuries later mathematicians in India began to use a circle to represent zero. They were the first to write numbers in columns. A blank column was represented by zero. This system was introduced into the Arab world in the 7th century and the Hindu word, sunya, meaning empty, was translated into Arabic as sifr. From this came the English word zero.

The idea of travelling beneath the sea inside a vessel is one that has been around for many centuries. As long ago as 333 BC, Alexander the Great is said to have gone underwater inside a glass barrel. It is reported that he saw whales and deep-sea life.

Over the centuries, many designs for submarines were made. One of the best known is that of Leonardo Da Vinci in the 16'h century. In 1578, a British mathematician and naval writer, William Bourne, designed a vessel with a wooden frame enclosed in waterproof leather which could be rowed underwater. It, like Da Vinci's submarine, was never made.

In 1620, Cornelius Van Drebbel, a Danish doctor, designed the first submarine to be built. His was also designed to be rowed underwater. Air was supplied through tubes that went up to the surface. This allowed his craft, also of waterproof leather, to be underwater for several hours. His submarine was tested in the Thames River in England. It travelled successfully at depths close to five metres. It is said that King James 1 of England rode in one of Van Drebbel's submarines to prove that it was safe. The British navy, however, was not interested in the invention.

In the first thirty years of the 18'h Century, there were numerous types of submarine patented around the world. New ways of submerging and resurfacing were introduced with the invention of ballast tanks. They were first used as warships in the American Revolution (1775-1783) and later in the American Civil War (1861-1865).