The Origin and Function of Bifocal Reading Glasses
Some people of an age of forty or older may have such an
experience that when they tried to buy a pair of reading glasses, the
seller or retailer recommended a pair of bifocal reading glasses which
was relatively more expensive. In fact, these bifocal reading glasses
have been in wide use for many years. A large number of elder
individuals have to rely on these devices while carrying out some of
their daily activities including recreations. However, there may be
still lots of users who do not know or have little information of two
points of these glasses. One is the origin and the other is the exact
function.
The most widely recognized origin of bifocal reading
glasses is that they are invented in 1794 by Benjamin Franklin who was
one of the founders of the United States. This great statesman had
trouble seeing both up close and at a distance when he was getting old.
During a long time, he had to use periodically two pairs of prescription
eyeglasses, one for close vision and the other for distance view. Of
course, this kind of practise was very inconvenient when he wanted to
switch visual ranges on a daily basis. A great man is always easier to
be driven to develop an alternative to the unsatisfying, current
solution. Benjamin was at that time also a great inventor. The first
pair of bifocal reading glasses was created by him by having both types
of the lenses fit into a single frame.
That was the same design of bifocal reading glasses that is widely seen today. The past two centuries have never witnessed a significant change in the basic design. Till now, the function of this kind of magic spectacles is quite clear that they can enable a wearer to see both near and distant objects clearly. This is achieved by combining a positive power and a negative power in a single lens. A bottom part of the lens is usually made for near viewing and the upper section is for distance vision.
That was the same design of bifocal reading glasses that is widely seen today. The past two centuries have never witnessed a significant change in the basic design. Till now, the function of this kind of magic spectacles is quite clear that they can enable a wearer to see both near and distant objects clearly. This is achieved by combining a positive power and a negative power in a single lens. A bottom part of the lens is usually made for near viewing and the upper section is for distance vision.
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