He improved magnification of microscopes by polishing lenses, by placing the middle of a small rod of soda lime glass in a hot flame, van Leeuwenhoek could pull the hot section apart like taffy to create two long whiskers of glass. By then reinserting the end of one whisker into the flame, he could create a very small, high-quality glass sphere. These glass spheres then became the lenses of his microscopes, with the smallest spheres providing the highest magnifications. Basic in design, van Leeuwenhoek's instruments consisted of simple powerful magnifying glasses, rather than the compound microscopes (microscopes using more than one lens) of the type used today or in Zacharias Jansen's original microscope design. Compared to a modern microscope, van Leeuwenhoek's design is extremely simple, using a single lens mounted in a tiny hole in a brass plate that makes up the body of the instrument. The specimen was then mounted on a sharp point that sticks up in front of the lens. Its position and focus could be adjusted by turning the two screws. The entire instrument was only 3-4 inches long, and had to be held up close to the eye, requiring good lighting and great patience to use.