Concrete can be said to have been used for thousands of years, if the words is taken generally to mean a hard building material produced from a mixture of cement, sand, gravel and stone. The Assyrians and Babylonians used clay to bind sand and stones, and the ancient Egyptians discovered lime and gypsum. The Romans mixed slaked time with volcanic …

On 17 January 1779 two ships of Captain James Cook anchored in Kealakekua Bay, Hawaii. The natives believed that in ancient times Lono, god of fertility and cultivated foods, came down from the sky. Lono was honoured in the Makahiki festivities that lasted from October to February. When Cook landed, the people greeted him as Lono. Priests brought offerings, and …

In the violent beginnings of our planet the surface of the Earth looked a terrifying place. White-hot magma, formed of molten rock from the Earth’s interior, boiled on the surface with constant explosions. At the same time showers of meteorites and cosmic dust, attracted by the pull of the Earth’s gravity, made the sphere grow bigger and bigger as it …

As it gradually cooled, the magma solidified on the surface and the Earth became covered with a crust of primeval rocks, mainly consisting of granite and basalt. These rocks encased our globe like a rigid shell, while inside it continued to be burning hot. When the Earth cooled still more it shrank, and the rocky layer which covered it had …

There is virtually no “best time” to launch a rocket to the moon, because, in terms of space travel, the journey is so short. The average distance is 238,000 miles, with a maximum variation of only 25,000 miles. A space shot, whether to the moon or some other object, is made by a rocket already in orbit. To take a …

Occasionally, civil wars occur which lead to a country being divided in two. For example, a war in Pakistan in 1971 led to the creation of the new nation of Bangladesh. Not all new countries, however, win international recognition. For instance, Cyprus has been divided, through the breakaway Turkish Republic of Northern Cyprus, established in 1983, is recognized only by …

Litmus paper turns red when placed in an acid solution, but blue if the solution is alkaline. This absorbent paper is the oldest and most commonly used indicator of the presence of absence of acid. Its special qualities are due to the fact that it has been soaked and impregnated with a mixture of dyes called litmus. The litmus mixture …

Apple scab occurs when an apple tree falls victim to a fungus called Venturia Inaequalis, a malignant growth which slowly eats away at the leaves and fruits. It is a widespread and serious disease affecting apple trees all over the world, but is more powerful in warm climates. Farmers control the fungus by spraying the trees with sulphur. That is …

A tree never permanently stops growing as long as it lives. But in most countries each year’s growth is ended during the cold and dry season. The annual period of growth depends on the climate. In most tropical regions a tree may grow continuously. Every period of growth is marked by an annual ring. This ring takes the form of …

A forest becomes petrified or turned to stone under certain conditions, through the action over the centuries of water containing large quantities of minerals. Tree trunks buried ages ago under mud, sand or volcanic ash have been gradually transformed as water seeped into the empty cells of the decaying wood, filling them with mineral matter and preserving every detail of …