This seminal work is a pioneering study of the relationship between mental and physical performance. It introduces a range of objective tests for assessing abilities such as memory, attention, and reaction time, and explores the implications of these findings for education, employment, and health. Despite being over 100 years old, this book remains a classic text in the field of psychology and an important source of ideas and inspiration. 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.