Optician more important and dignified. Far-sighted or aging colonial Americans imported spectacles from Europe. Spectacles were primarily for the affluent and literate colonists, who required a valuable and precious appliance. Benjamin Franklin in the 1780s developed the bifocal. Bifocal lenses advanced little in the first half of the 19th century. The terms bifocal and trifocal were introduced in London by John Isaac Hawkins, whose trifocals were patented in 1827. In 1884 B. M. Hanna was granted patents on two forms of bifocals which become commercially standardized as the "cemented" and "perfection" bifocals. Both had the serious faults of ugly appearance, fragility,
Letter to M. D'Alembert on Spectacles Letter to M. D'Alembert on Spectacles Letter to M. D'Alembert on Spectacles () is a 1758 essay written by Jean-Jacques Rousseau in opposition to an article published in the "Encyclopédie" by Jean d'Alembert, that proposed the establishment of a theatre in Geneva. More generally, it is a critical analysis of the effects of culture on morals, that clarifies the links between politics and social life. Rousseau relates the issue of a theatre in Geneva to the broader social context, warning of the potential the theatre has to corrupt the morality in society. The "Letter" is considered to be highly personally