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 compound microscope was invented in 1590, 40 years before van Leeuwenhoek was born. The simple microscope was invented 300 years earlier. Around 1670, van Leeuwenhoek invented a method for making small spherical lenses that much increased magnification of simple microscopes.