Zacharias Janssen was a glasses maker. He is credited for making the first microscope. Many people speculate that his father, Hans, had an important role in helping Janssen to create it. He is also credited to have invent the telescope.
Anton van Leewenhoek
Anton van Leewenhoek had no higher education and did not attend a university. Many people say that the only reason he is considered a scientist is because of his curiosity. He had invented a microscope which was probably just a powerful magnifying glasses. The entire instrument made was only 3 or 4 inches long.
He built one of the best microscopes in his time. He observed a cork from an oak tree and saw empty spaces which were shaped as rectangles. He name them cells, which means small rooms. He calculated almost 12 hundred milloin cells!
Sir Isaac Newton
Sir Isaac Newton improved the microscope because he developed a theory that explained how light moved. This helped microscope builders improve their work. Hooke and Newton were considered scientific rivalries and didn't agree on many things.
He declared that all cells are the basic unit for plants.This was one of the most important discoveries that contributed to the cell theory.
He was a German psychologist. He contributed by defining the cell as the basic unit of animal structure.