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.
Answer   Microscope was invented by ZACCHARIAS JANSSEN a DUTCHMAN in 1590. From 1632-1723 ANTON VAN LEUWENHOEK was getting better results with a powerful single lens, whiâ¦ch he made himself. He was a dry goods dealer who made lenses as a hobby. Leuwenhoek kept his method of lens making a secret.