who invented the lightning rod and bifocal glasses
Bifocals
Original bifocals were designed with the most convex lenses ( for close viewing ) in the lower half of the frame and the least convex lenses on the upper . Up until the beginning of the 20th century two separate lenses were cut in half and combined together in the rim of the frame . The mounting of two half lenses into a single frame led to a number of early complications and rendered such spectacles quite fragile . A method for fusing the sections of the lenses together was developed by Louis de Wecker at the end of the 19th century and patented by Dr. John L. Borsch , Jr. in 1908 . Today most bifocals are created by molding a reading segment into a primary lens and are available with the reading segments in a variety of shapes and sizes. The most popular is the D - segment , 28 mm wide ( citation needed ) . While the D - segment bifocal offers superior optics , an increasing number of people opt for progressive bifocal lenses .
Original bifocals were designed with the most convex lenses ( for close viewing ) in the lower half of the frame and the least convex lenses on the upper . Up until the beginning of the 20th century two separate lenses were cut in half and combined together in the rim of the frame . The mounting of two half lenses into a single frame led to a number of early complications and rendered such spectacles quite fragile . A method for fusing the sections of the lenses together was developed by Louis de Wecker at the end of the 19th century and patented by Dr. John L. Borsch , Jr. in 1908 . Today most bifocals are created by molding a reading segment into a primary lens and are available with the reading segments in a variety of shapes and sizes. The most popular is the D - segment , 28 mm wide ( citation needed ) . While the D - segment bifocal offers superior optics , an increasing number of people opt for progressive bifocal lenses .