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.
Zacharias Janssen is the Dutch spectacle maker who is widely credited as the inventor of the first compound microscope. Although many of the archives surrounding Janssen's invention have been lost, historians believe that Zacharias and his father Hans invented the first microscope at some point in the 1590s.