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To the Editor:
—Apropos of Dr. David G. Cogan's article on "Some Ocular Phenomena Produced with Polarized Light," in the March 1941 issue of the Archives (Arch. Ophth.25: 391 [March] 1941), I wish to make a few remarks concerning polarized light.Prior to the revolutionary invention of polaroid by Edwin H. Land, of the Polaroid Corporation, investigators in the field of polarized light employed Nicol prisms of calcite. Polarizing accessories were constructed for the biomicroscope and the ophthalmoscope, and several papers have appeared giving details of ophthalmic studies. In fact, a Nicol polarized ophthalmoscope devised by Cardell in England has been sold commercially. Nearly all the problems of the optics of polarized light had been worked out prior to Land's invention—which provided the long-sought wide aperture polarizing contrivance—and now a resurgence of interest in this absorbing field of optics is well on the way.Professor B. Strampelli, of the