In January 1909 a friend of the Scientific American paid the sum of 500$ which was to be awarded as a prize for the best popular explanation of the Fourth Dimension. The object being to set forth in an essay not longer than 2500 words the meaning of the term so that the lay reader could understand it. 245 essays were submitted, the 500$ prize was awarded to Lieut.-Col. Graham Denby Fitch, Corps of Engineers, USA, and the essay was published in the Scientific American of July 3rd 1909. Despite the character of the subject, extraordinary interest was manifested in the contest. Competitive essays were received from almost every civilized country. Because of this unexpected interest in the subject, it has seemed advisable to preserve a few of the essays which were submitted. Prof. Henry P. Manning (Brown Univ.) has chosen essays which lend themselves best for the purpose of a popular book on the Fourth Dimension, in other words, those which present the subject from as many different points of view as possible. This book contains 22 of the submitted essays, starting with the prizewinning one, followed by three that received an honorable mention. (Summary adapted from the preface by Availle).