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.
â¢ Had to have a microscope first. o Invented in 1595 by Zacharias Janssen  Was considered a toy for the rich. â¢ Anton Van Leeuwenhoek 1670âs o Improved the microscope so much heâs considered the father of the microscope. o First looked at water under a microscope o Discovered small animals.