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.
Simple Answer: Antonie (Anton) van Leeuwenhoek made an estimated 500 lenses over a period of 50 years which were incorporated into about 200 microscopes that he constructed. â¦ Nine of his microscopes still exist. He also enhanced the overall design of the simple microscope and specimen holder.