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 magnifying glass was invented by Roger Bacon in 1250 Hypernyms (magnifying glass is a kind of...): light microscope (microscope consisting of an optical instrument that magnifies the image of an object) Hyponyms (each of the following is a kind of magnifying glass): jeweler's loupe; loupe (small magnifying glass (usually set in an eyepiece) used by jewelers and horologists)