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.
At this time, Dutch spectacle makers were experimenting with multiple lenses. Telescopes were invented in this way. By reversing a telescope the microscope was discovered! Credit for the first microscope is usually given to Zacharias Jansen in Middleburg, Holland around 1595. The Jansen microscope was composed of 3 sliding tubes, measuring 18 inches long when fully extended and 2 inches in diameter.