Answer: 20 years. Furnaces should last between 15 and 20 years, according to industry experts and the Department of Energy. Furnace filters, however, only hold up one to three months â and in order to avoid an expensive service call, it's crucial to change them on the manufacturer's schedule.
Lens Improvement. Later in the 16th century, Anton van Leeuwenhoek began polishing and grinding lenses when he discovered that certain shaped lenses increased an imageâs size. The glass lenses that he created could enlarge an object many times.
The first big microscopy advances came in 1665, when Robert Hooke published theMicrographia, a collection of copper-plate illustrations of objects he had observed with his own compound microscope. He coined the term cell when looking at a piece of cork under 30x magnification. In the late 1660s, Antony van Leeuwenhoek began to grind his own lenses and make simple microscopes. Each microscope was really a powerful magnifying glass rather than a compound microscope.