Lenses and the microscope

Our eyes can only see things above a certain size. For a long time, a whole world of tiny things stayed hidden.

Long ago people found that a curved piece of glass, thick in the middle and thin at the edge, makes small things look bigger. That shape is just like a lentil seed, so the glass was called a lens.

Try it (Activity 2.1). Fill a round glass flask with water, cork it and stand it on an open book. The letters under it look bigger: the flask of water works like a magnifying glass. Then look at an ant through a real magnifying glass and see the parts of its body.

Lenses got better and stronger over time, from simple magnifying glasses to the microscope (micro means very small).

In 1665 Robert Hooke published a book called *Micrographia*, full of careful drawings of tiny things nobody had seen before. His microscope made things look 200 to 300 times bigger.

He looked at a thin slice of cork (the outer bark of the oak tree) and saw lots of small, empty boxes, like a honeycomb. They reminded him of the small rooms monks lived in, which were called cells. So he called each box a cell. It was the first time the word was used in science for the basic unit of life.

Around the same time, in the 1660s, a Dutch scientist, Antonie van Leeuwenhoek, made better lenses and more useful microscopes. He was the first person to clearly see and describe tiny living things such as bacteria and blood cells. That is why he is called the Father of Microbiology: micro (very small) + bio (living things) + logy (study).