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 History of the microscope. An introduction to Microscopy. It is not quite certain who invented the microscope. Probably, spectacle makers in Middelburg, The Netherlands, invented both the compound microscope and the refracting telescope, between 1590 and 1610. The names most mentioned are those of Hans and Zacharias Janssen. The first well known users were van Leeuwenhoek and Hooke.