Transcriber’s Notes: Underscores “_” before and after a word or phrase indicate _italics_ in the original text. Small capitals have been converted to SOLID capitals. Illustrations have been moved so they do not break up paragraphs. [Illustration: =SKI-OPTOMETER MASTER MODEL 215= Embodying in a Single Instrument, in Convenient Form, Cylindrical and Spherical Lenses, in Combination with Appliances for Testing and Correcting Muscular Imbalance.] Refraction and Muscular Imbalance _As Simplified Through the Use of the Ski-optometer_ By DANIEL WOOLF WOOLF INSTRUMENT CORPORATION NEW YORK: 516 FIFTH AVENUE Copyright 1921 By WOOLF INSTRUMENT CORPORATION Published by THEODORE S. HOLBROOK NEW YORK CONTENTS CHAPTER I Page SKI-OPTOMETER CONSTRUCTION 1 Convex Spherical Lenses 2 Operates and Indicates Automatically 6 Concave Spherical Lenses 7 CHAPTER II CYLINDRICAL LENSES 10 Obtaining Correct Focus 11 Why Concave Cylinders Are Used Exclusively 14 Transposition of Lenses 14 CHAPTER III HOW THE SKI-OPTOMETER ASSISTS IN REFRACTION 17 The Use of the Ski-optometer in Skioscopy 17 A Simplified Skioscopic Method 20 Employing Spheres and Cylinders in Skioscopy 22 Use of the Ski-optometer in Subjective Testing 23 A Simplified Subjective Method 24 Procedure for Using Minus Cylinders Exclusively 26 Constant Attention Not Required 29 CHAPTER IV IMPORTANT POINTS IN CONNECTION WITH THE USE OF THE SKI-OPTOMETER 30 Elimination of Trial-Frame Discomfort 30 Rigidity of Construction 31 How to Place the Ski-optometer in Position 32 Cleaning the Lenses 33 Accuracy Assured in Every Test 34 Built to Last a Lifetime 35