Book excerpt: In this classic work on light and vision, Lloyd provides a comprehensive overview of the properties of light, and how they are perceived by the human eye. He also discusses the properties of lenses, mirrors, and other optical instruments, and provides practical advice on using them for various applications. This book is essential reading for anyone interested in optics and its applications in fields such as photography, astronomy, and medicine. This work has been selected by scholars as being culturally important, and is part of the knowledge base of civilization as we know it. This work is in the "public domain in the United States of America, and possibly other nations. Within the United States, you may freely copy and distribute this work, as no entity (individual or corporate) has a copyright on the body of the work. Scholars believe, and we concur, that this work is important enough to be preserved, reproduced, and made generally available to the public. We appreciate your support of the preservation process, and thank you for being an important part of keeping this knowledge alive and relevant.