The Economy of the Eyes - Precepts for the Improvement and Preservation of the Sight; Plain Rules Which Will Enable All to Judge Exactly When, and What Spectacles Are Best Calculated for Their Eyes; Observations on Opera Glasses and Th... #269751

Explanation of the Plate fronting the Title<br><br>Fig. I. Is the Spectacle front recommended for Eyes in general; the distance between the centres of the openings which held the Glasses being 2 1-2 inches, i.e. the average distance between the centres of the Eyes.<br><br>Fig. II. Is a portrait of the Pupil of the Eye when in a state of expansion. See Chapter XII. page 73, and No, X. of the Appendix.<br><br>Fig. III. The Pupil in its most contracted state. See page 73, &c.<br><br>Fig. IV. Convenient double Folding Hand Spectacles. See page 20.<br><br>Fig. V. A Preserver, or the First Sight for Long Sighted Eyes, i.e. a Convex lens of 36 inches focus cut in half to shew its form, c.the thickness of it at the middle and at the margin of it. See page 27.<br><br>Fig. VI. The 8th Sight, for Long Sighted Eyes or 12 Inches focus. Fig. VII. No.1 Concave, or the First Sight for Short Sighted Persons. See Chapter XIII. page 85.<br><br>Fig. VIII. No.12 Concave, or the 12th Sight for Short Sighted Persons.