Bifocal
The Optical Dictionary · 1904 · p. 3
Having two foci. Bifocal Lens.—A lens, the upper half of which is adapted for viewing distant objects, whilst the lower half is adapted for viewing near objects.
Bu kavram başka kaynaklarda da geçiyor
An Illustrated Dictionary of Medicine, Biology and Allied Sciences (1907)
The Student's Medical Dictionary (1896)
An Illustrated Encyclopedic Medical Dictionary (1894)
Readham'da tam maddeyi gor →