MESSRS EDITORSOn page 235, this volume, SCIENTIFIC AMERICAN, I observe that one of your correspondents has discovered that he is "lonrsighted with his left eye, and shortsighted with his right eye, and asks if this is a common occurence ?" I would say it is not a common occurrence, although I have met with some twenty or thirty instances of it In the winter of 1831, a lady between forty and fifty years of age, came to my jewelry store in Burlington, Vt, where, after some hours' trial, I succeeded in suiting her eyes, by fitting a convex glass of twelve inches focal distance from one eye, and a concave glass, No 12, from the other eye, when the lady declared she could see with both eyes alike A gentleman in this city now wears his spectacles with a convex glass of some twelve to fifteen inches focal distance for one eye, but uses no glass for the other eye These were all caused by nature, not by accident To determine whether the eyes are "mates," take a pair of convex spectaclesif longsightedand look upon fine print, and observe whether each takes in the same number of lines, and if the same appear to be straight If shortsighted, take a pair of concave glasses, and look at a brick wall across the street, and observe as above The difference between the two eyes, if any, will at once be noticed R FITZGERALD New Haven, Ct, April, 1858