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.
He coined the term âcellâ when looking at a piece of cork under 30x magnification. In the late 1660s, Antony van Leeuwenhoek began to grind his own lenses and make simple microscopes. Each microscope was really a powerful magnifying glass rather than a compound microscope. Leeuwenhoekâs hand-ground lenses could magnify an object up to 200 times! He observed animal and plant tissue, sperm cells and blood cells, minerals, fossils, and much more. He also discovered nematodes and rotifers (microscopic animals), and he discovered bacteria while looking at samples of plaque from his own and othersâ teeth. 1700-1800s: Not much change in the basic microscope design occurred, but better lenses were crafted (using purer glass and different shapes) to solve problems like color distortion and poor image resolution.