so lignes stands to the unknown distance, which consequently is )/ or and subtracting Iignes from you will find that the image of an object that is two feet away is closer to the lens by about Iignes, and that according to our assumption, therefore, which is hardly exact, the retina would have to be lignes closer to the crystalline lens in order to distinctly see an object two feet away than to see an object a half foot away.