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.
When the microscope was invented around 1590, suddenly we saw a new world of living things in our water, in our food and under our nose. But it's unclear who invented the microscope. Some historians say it was Hans Lippershey, most famous for filing the first patent for a telescope. Other evidence points to Hans and Zacharias Janssen, a father-son team of spectacle makers living in the same town as Lippershey.