We do not know exactly when man first discovered that objects seemed much larger when seen through a specially shaped piece of glass. There are some very old stories but they are all vague. The known history of the microscope begins in the seventeenth century when the Dutchman, Anton van Leeuwenhoek, invented a simple microscope consisting of a single lens with a relatively high magnification. The first compound microscope was devised in 1590 by Zacharias Janssen.

The word microscope comes from the Greek micros meaning small and skopeein meaning ‘to look’. The instrument works with two lenses or discs of glass. The upper lens is the eyepiece and the lower one is the objective. The objective lens magnifies the object and the eyepiece lens enlarges the magnification. In modern instruments both the eyepiece and the objective consist of several lenses, so arranged that they rectify the distortion caused by the curvature of the glass.

The objects to be examined are placed on a glass slide. These objects are cut very thin so that light shines through them. In a microscope the light is reflected through the objects by a mirror. Scientists also use electronic microscopes which can magnify objects millions of times.

The basic parts of a microscope are the condenser which illuminates; the focusing mechanisms operated by coarse or fine adjusting screws; and a variable diaphragm that controls the amount of light that goes into the condenser.

Gnus are mammals that live mostly in central and southern Africa, grazing on the grasses and low scrub of the open plains. At one time there were many herds of them. They are very sociable animals and often mingle with herds of zebras, ostriches or antelopes.

Whenever strange intruders appear the gnus behave in a rather odd manner. They ruffle up their fur, paw the ground and go into a thundering charge. But after going only a short distance they stop, wheel round and see what effect their display is having. If the charge has made no impression then the gnu beats a hasty retreat. However the thundering sound of hooves of a charging herd of guns is often enough to drive away any intending attacker.

The gnu is a ruminant and a very strongly built animal. In South Africa it is kept on farms like a domestic beast. Its body resembles that of a horse but its head is very large and covered in a thick tuft of hair. It has a pair of sharply curving horns which are very thick at the base.

During the mating season penguins gather together by the tens of thousands along the coasts of Antarctica. The female penguins lay one or two eggs which they place in a hollow in the ground. They take turns with the male penguin to sit on the eggs, clutching them tightly between their legs and their downy stomachs.

With the eggs covered like this, the penguins can still move from place to place although they look extremely odd when they do so. When the female is sitting on the eggs, the male bird feeds her. He continues to do so for a time after the young birds are hatched.

There are seventeen species of penguins. They vary in height from 40 centimeters to more than a meter. They all live in the southern hemisphere and go on long migratory swims to escape severely cold weather.